I'm toying with the idea of adding little, basic quizlets to the ends of my lectures for which students would be immediately responsible.
The questions would purposefully not be difficult. They'd be more on the level of, "were you paying attention to what we just did?" Basic recall, simple factoids, etc.
I'd advise against this. While it sounds like it directly addresses the problem, it's liable to backfire and exaerbate the issue.
While this test would create an obstacle for the willful slackers, it's also going to become an obstacle for students you're not intending to target: students having an off day, students struggling with the material, students who doubt their own skills until they feel they've got a grasp on things, ... These students are all going to feel pressure during your lecture knowing that an inevitable quiz is coming at the end of the lecture.
I suspect your response to this may be along the lines of
"I'm only going to ask them to repeat the lecture, not to have them show they fully grasp it."
But then your quiz is going to be about the lecture itself, not the material that the lecture is about. A student who is ahead of the curve and already understands the current topic might be justified in allocating their time and effort towards other courses they are in fact struggling with, but now you're requiring them to mimic your words back to you. Taking it even further, they could even be helping someone next to them, thus missing particular things you've said.
Comparatively, if you did your quiz at the start of the next lecture, then your quiz can focus on the material more than the actual lecture itself. This enables the "expert" students to not have to listen to you explain something they already understand; and the "slower" students have had a week's time to catch up on anything they may have sturggled to understand the first time.
In a way, quizzing someone directly after your lecture is asserting/guaranteeing that you are able to perfectly explain something and have people immediately understand it. Even if that is not the goal of the quiz, your students will perceive this to be the goal, and it is going to create (possibly unspoken) friction for them.
(1) are quizlets a good solution to my problem?
And (2), if they are a good solution, is there any wisdom from the trenches on how to pull these together so that they are effective without bringing on substantially more grading work? I'd like to make them as useful in the learning process as they can be, but I have to be careful about what I take on.
The short answer: It would be wrong for you to cater your curriculum so that students can instead focus on other courses. However, countering this by cracking down on student focus is not a good solution and is likely going to exacerbate the issue for the students.
We've all had teachers who felt entitled to continue the class after the bell rang. We've also had teachers who were sticklers for arriving to class on time. Both teachers can argue that their expectation is reasonable. But a student who is forced to stay late in one class and thus be late for the next one, is going to resent both teachers because pleasing one teacher would get them in trouble with the other teacher.
If you double down on student focus, that's essentially what you're doing. To the students, it will come across as a NIMBY-like "my course is more important than the other ones!".
There is an alternate solution here that alleviates the issue for students: optional quizzes that focus on the subject matter (not the lecture) and what you will be testing for during the end of unit quiz. The implicit suggestion is that "when you can answer these questions, you have grasped the essence of the subject matter".
For students who are struggling with other courses, are having trouble grasping the subject matter, or simply those who are succumbing to stress, this create a pressure-free guideline on the important points to take away from your lecture.
For students who already master the subject matter, they can be used as a way to reaffirm that they understood the full subject matter of the lecture and didn't miss a smaller chunk that is in fact new to them.
This enables them to very quickly identify that they don't need to go through this any deeper and thus can focus on other courses where they're not ahead of the curve. This is a major boon to relieving stress, because it cuts out "wasted" time (mind the quotes) that they could've spent better.
For this reason, some lecturers in college (when I was a student) used to start the lecture off with such a quiz (merely presenting it, not actually handing out sheets). Anyone who knew the answer to all questions was free to leave (it was up to the students to decide for themselves), because they wouldn't learn anything new during that lecture and could instead take the time to dedicate effort towards classes where they did need to catch up to the curriculum. This of course assumes you're in an educational context when attendence is not mandatory.
You can, if you want, enable students to hand in these optional quizzes. This mean it's up to the student to decide whether they want/need your feedback. The request for help from these students is going to outweigh the effort of having to grade (I sincerely hope). Other students who are already confident in their grasp of the subject matter won't bother with the optional quizzes and thus won't require you to go through the effort of marking those (trivial to the students) quizzes.
Any student who does not grasp the subject matter, does not ask for help and does not self-test themselves will be caught out by the end of unit test. However, any approach that would catch these students quicker (e.g. at the end of the lecture, as per your goal) would also create an obstacle for other students.
In short, you can't police daydreaming. And even if you could, the rigorous nature of your policing is going to cause more issues than it solves.