Do you need a hydrostatic release?
If you have a commercial vessel, yes. The Coast Guard requires one.
For recreational vessels the answer is not cut and dry. Hydrostatic Release Units (HRU) work by water pressure, releasing the life raft (or EPIRB) when the unit gets about 12 feet below the surface. In order for a HRU to work effectively the life raft needs to be able to float to the surface once released. If the vessel is on her side this might not happen or if you have rigging over the life raft that too might also impede the trip to the surface. So in order for your raft or EPIRB to deploy properly when relying on a HRU requires good luck.
Fire is a major cause of recreational vessel sinkings/abandonments. If you have a fire you will be deploying your life raft manually. You don't want to wait for the vessel to sink, it's time to bug out. Having your raft located in a position to allow easy manual deployment is much more important than having a HRU. Actually this is a good argument for having a raft packed in a soft valise that can be stored in an easily accessible location.
HRU's require maintenance, which is actually replacement every two (2) years. This adds about $75.00 to your annual maintenance budget. Like all things mechanical, being around salt water and in a high UV environment means corrosion and plastic degradation. If you are going to have a HRU, it might as well work.
So, would I have a HRU on my own boat? If I was going offshore, yes. For coastal or inshore work I would put the money to better fire extinguishers. I would much rather stay on my boat even if it was unable to move than have to get in to a life raft.