I presently own two brazilian rainbow boas and they are by far my favorite reptile to keep. The "difficulty" that most people talk about isnt actually very hard at all... a Rainbow boa really only requires three things...
A) water/humidity proof/tight cage. Whatever you do, dont use mesh and dont use melamine. Mesh screens allow too much humidity to exit the cage, and melamine will rot and decay with the high humidity needed to keep them healthy.
It sucks for viewing but I use two plastic totes from Rubbermade. I've had one snake escape once and since then I added weight to the lid and have had no issues.
B) they need to be misted daily. If you don't/arent diligent about it, they will quickly develop respiratory infections and can die in almost no time.
If you like to or have to travel....This is not the snake for you. I sacrificed many trips because there are very few people I trust enough/know enough about them not to let them die.
C) they need to be handled on a very regular basis. A lot of people that are trying to rehome their rainbows are doing it because they have become aggressive from lack of attention and are no longer pleasurable to own.
Having said all of that.... If you get the right cage, made of the right material, and you mist or have a mister set up than the humidity issue no longer becomes a problem. They are sensitive to high temperatures, so don't overheat them, low/ mid 80s is fine for an adult. Other than that.... they arent any different than any other snake. ONLY GORGEOUS.
Neither of mine have ever tried to bite me. I got one as an adult and waited to get one that I was told was friendly (I'm not a fan of aggressive snakes personally). The other I got as a juvenile, and even though i was warned that she was nippy, has still never tried to bite me and I've had her about 6 months now.
I highly recommend Brazilian Rainbow Boas, and i hope you arent discouraged by the extra care, because they really are just amazing animals