I recently completed training for a Dive Rite Optima Rebreather I purchased and have completed over 20 dives on it so far. Prior to that, I have done all types of diving, including deep wreck diving on trimix, and I am also certified as a PADI Open Water Instructor.
You are correct in that the rebreather takes a lot more set-up and breakdown time than normal open circuit. The initial cost and ongoing costs are also much greater than normal oc scuba, and while diving, you also have much more to worry about.
However, the amount of versatility that it provides is awesome. For example, the other day we did a dive in 140 feet of water and was able to stay down for approx. 45minutes, with limited narcosis, b/c I had a lite trimix mix as my diluent. Sure, I still had to deal with the decompression, but that's not a problem with the rebreather. With my unit, I carry enough gas to stay down approx 4 hours, regardless of the depth, and the way I have my rebreather is configured, I only carry 26 cubic feet of gas within the rebreather, so it is reletively lite (approx 40+ pounds). When I'm on a boat doing a 3 tank dive, I do not have to switch tanks between dives. I also do not exhale any bubbles, so the marine life is generally not so intidated by my presence.
With regards to safety, it's really not as unsafe as you have been led to believe. With proper training, you are taught to be conscious of everything you must be monitoring during the dive, and it becomes habit. Also, I ALWAYS carry sidemounted bail-out tanks with enough gas to complete all decompression and get me back to the surface, so if I have any type of problem, I simply bail-out. The extra time in preparing your gear, is because you are assembling the unit from scratch each time, and confirming that each componect is secure and working as it should be - how often have you really done that with your oc gear? Also, as priviously mentioned, if you do have a problem underwater, you generally have several different opions to deal with the problem, which if you develop good habits through proper training, it ends up being much safer than open circuit scuba.
With my rebreather, I dive with three computers and four independent sensors monitoring my oxygen (P02) at all times, and I have a small heads-up display located at the right hand corner in front of my mask, signaling my current oxygen (P02) at all times.
Many manufacturers are offering rebreather experiences from time to time, where you can get in a pool and try one out. If your are at all curious, give it a try. If you decide to go with it, you will end up spending LOTS of cash, but if you can swing it, YOU WILL NOT REGET IT - I HAVEN'T!
Safe Diving,