Make sure you read up on the operating characteristics, some of the personal epirbs won't transmit well if the ant. isn't manually unfolded. They also won't float on their own with the ant. in the upright position. This might or might not be a concern depending on what your expectations are. I went the ACR globlefix II. This unit has internal gps and will float with the ant in the upright position. It also will auto activate if it is gets wet and is out of it's bracket. It will not auto activate if it gets wet while in the bracket.
I initially was looking at the ACR 406 aqua fix PLB, but after reading about it's limitations ( ant needs to be unfolded for best reception and must be held in the upright position) I decided in an emergency situation those were things I didn't want to have to worry about.
I went with the Cat II (cat I will auto activate and deploy from bracket if it submerges below 13 feet) because at the time I purchased it I was boating on a foam filled center console that wouldn't/shouldn't fully sink. If I were purchasing today I would get the Cat I for my Hatt. (and still might get one)
I think the PLB's are a good "Personal" epirb. An item you carry in you own bag as a supplement to the boat's primary epirb, or if you boat with various other people on different boats and want to carry your own. But every offshore vessel should have a primary Cat I or II mounted epirb.
In my opinion, the diff in price of the PLB (aprox $500 -$600) vs. a cat I or Cat II ($800 -$1100), is a non-isuue. You should buy one based on your use and needs, not price. If you cant afford an EPIRB, you don't need to be boating offshore (in my humble opinion).
I'll get off my soapbox now, but I think too many people spend gobs of money on boats and boating gadgets for pleasure and comfort, then nickel and dime the safety equipment.
Just ask yourself: If your boat was sinking 100 miles offshore, what would you give for a device that would call the coast guard and give them you exact position every few minutes for 48 hours?
Just my thoughts,
Benjy