I have a sleep tent and can tell you what I know about them.
Firstly, you should probably try to avoid giving them to a female bird. It can seem like a safe enclosure, which could lead to egg-laying. If you really want some kind of hiding spot, you should get a tent that is bottomless and ties to the top of the cage (like this: http://www.parrotdiseperch.com/parrot/shop_details.php?prod=1781
) or a swing with a hut on it (also bottomless).
If your bird is prone to laying, you should probably avoid an enclosure all together.
As for a male, it's okay but you need to watch a few things:
1) Watch out for tent deterioration, you don't want your bird to be caught. Trim any lose threads or pilling. You should replace it once it is worn out.
2) If your bird starts to become aggressive around the tent, you should remove it when the bird is away. This might be especially pronounced when hormone season is in full swing.
I also prefer the tents with a hard, cardboard or plastic (covered in fabric) bottom. The soft bottomed ones are okay with full supervision, but you can't watch your bird all night. I would also get a tent that is open on both sides, a closed back seems very dangerous to me.
The only bird of mine that uses a tent is my lovebird. He has a hard-bottomed one that is plain fabric on the outside and fleece on the inside, I check it reguarly for wear and I can wash it as well. I cannot remember the company at the moment, but it is a small one from the United States (everything is hand made). I think these would be pretty easy to make yourself if you can sew.
I have heard of accidents with sleep tents but they seem to be due to poor design (I think the Happy hut brand is the big culprit) and/or lack of maitenance. *ALL* of our birds toys can be dangerous, we have to inspect them regularly and supervise as much as possible to avoid injury, just like small children.