They are small as CAVX points out as well as the the other issues he mentions. If that's not a deal breaker then I would say yes they are probably one of the better solutions for DIY. Throw distance will matter with these prisms, my projector is at about 14' from the screen and this allows for about 1/3 of my zoom range to be usable with the prisms in place.
As far as a case, you can find various DIY examples out there if you search. The thread here has what I did which has worked out nicely with easy latch access. Final product on page 7. Also at the beginning of the thread I linked some dimensional drawings that may aid you in making your own case. If I recall correctly I had to shrink the case/lens template on a copier by 10% to make it the right size.