16-second loopers

[Kelly Coyle <kellycoyle@charter.net>]

I've been on and off this list for years, as my looping interest waxes 
and wanes -- usually I lurk, but I have a question that doesn't seem to 
have been addressed in the archive; so here:

I've had all of the "major" units (none now, though) -- EDP, Jamman, 
Boomerang -- so i have an idea how the tap to record, tap again to loop 
system works. But I've never used the sort of looper that you have to 
pre-define the length before you start. I'm kind of interested in those 
these days, either the EH reissue thing or the Maneco variations. So 
tell me, how do they work in practice? How do you know how fast to 
play, when the loop is going to kick in? (Do they send a click or 
something? Flashing lights?) Or do I misunderstand how they work 
altogether?

After that, I'm interested in how that approach works for people. (I 
realize, at least with the EDP, that you can do it this way too.)

Thanks.