I don't think H-valves are that unreliable either. If they were, they wouldn't be allowed at the Intro Cave level and we have yet to have a fatality of a Intro Cave diver wearing a single tank (that I'm aware of).
There are a few disadvantages, one being that you will have difficulty renting H-valve tanks from any random dive shop but your regs will be set up specifically for using one. That can cause logistical problems in some situations--just try doing a 2-tank dive day with a K valve on one tank and a H valve on the other. Also, in order to be of any benefit you have to be able to do a valve shutoff quickly in the event of a problem.
I used to be all for H valves and didn't like pony bottles, but after rebreather training with bailouts I'm starting to see the advantages of a pony (which is really just OC bailout for OC equipment): no one gas failure can possibly jeopardize your life and require immediate action, no reliance on a buddy is required, and you can assist other divers by handing off a slung pony to them instead of being tethered with a hose air-sharing. Most of these advantages really don't come in to play in true recreational diving, though, and there are a few skills that are good to know concerning stage bottles to really take advantage of all this.