I have purchased one, any thoughts on them?

I think they may be a very good idea for some,
but I can't use them because my cages are double hung.
I also feel that the cage floor may be compromised
by cutting the hole for the drop down nestbox.
While on the other hand part of the cage floor is taken up
by the nestbox which is placed inside the cage.
It's a case of "six of one and half a dozen of the other".
Perhaps you should experiment with onme cage and see how it works for you.
Ottersatin.

that is my plan...

I have used them and i liked them but i dont have room too use them in my basement.I lost no babies drug out of the nest box.

I have been looking into this as well, and I think I am going to do the drop nest boxes. Since I won't be home during the day to check on them often, the drop nest box makes sense to me. Check out this site, www.kralek.com, and specifically this article...
http://kralek.com/Articles/LargeRabbitry.pdf
I especially like the way he uses a combination of drop wire and nest box so that you can remove the nest easily to check the kits, or take them inside in inclement weather.

Lots of good info there, and I think that you could also make a small "flap" of floor wire to cover the drop nest box when you did not need it.