I think they're a good idea, especially where you have sensitive neighbours and thin walls or need some separation when tracking with other instruments live.
But if they don't give you the sound you require or close, then they're useless. I built a variation of one in which I housed a box within a box and into the inner box, I place the amp. I can get pretty loud and the recorded sound is nicely raw. It takes a while getting all the settings as I want them though.