It looks as if this is exactly the same - electrically speaking - as a backstay antenna. The wire length is 34'. This is full wavelength for 10 meters and quarter wavelength for 40 meters. You will still need an antenna tuner and an RF ground to transmit on multiple bands.
They mention "insulation from RF shock hazards." These hazards are tiny, compared to RF burn hazards. You will NOT be protected from RF burn hazards. Don't stand close to any radiating antenna when transmitting. This doesn't apply to me because my brain is already fried.
Pros:
Easy to install. Comparatively.
Fewer "points-of-failure" in your rig (although backstay insulators are stronger than your backstay.)
Transferable to another boat with a little effort
You may get a small performance improvement due to the copper conductors. Yes copper is way more conductive than SS, but that's like saying a Ferrari is much faster than a VW bug when the speed limit is only 25 mph. It really doesn't matter.
Less maintenance on the copper/SS joint at the backstay.
Cons:
Windage.
Weight aloft.
Cost: you'll have to ask them.
Gordon West says: "No discernible losses." Not exactly a resounding endorsement, but neither is it damning. The drawbacks are windage and weight aloft. I would also keep a close eye on that heat shrink tubing at the base. If you contact them, I would ask whether they use tinned wire. They will probably say it isn't needed because the entire antenna is protected with insulation. At this point I would become skeptical.
A ~much~ cheaper alternative is a dipole. You can make the whole thing yourself for not much money., but it isn't as convenient to use. It must be hoisted to use. Performance is better than longwire, and no groundplane is required. It can work without a tuner; but if you don't have a tuner, you would need several dipoles to work multiple bands. Lifeline wire makes a good dipole. For myself, I recommend having a tuner for sheer versatility and convenience.
For a much longer discussion of alternatives, join the discussion board at Seven Seas (you don't have to be an SSCA member to use the board - same as here in HCOA.)
http://forum.ssca.org/phpBB3/ucp.php?mode=register
Then, under Tech Talk / Communications, check out
SERIOUS HAM SSB SETUP ON THE CHEAP
http://forum.ssca.org/phpBB3/viewtopic.php?f=5&t=2264
There are a lot of side trips in this thread. Be on the lookout for the ones that tell how to construct the antenna(e).
Have a little fun. Do the dipole for pennies on the dollar before you decide to go with a higher priced alternative.
Inspired by Clinton, you'll hear more than one ham say, "It's the antenna, stupid." Others like to say that the three most important things in getting a signal out are 1) antenna 2) antenna 3) antenna.
I don't think the Gam antenna is any better than a backstay antenna, and from an electrical point of view, it is no worse. You'll have to decide whether the other attributes tip the scale against the windage and weight aloft.
73 de N7LZ