We have this seat and really like it. It's much like the Britax Marathon, but the fabric isn't quite as nice (and not as many choices of fabric), and it doesn't have the little lap pad. We just took the lap pad off of the Roundabout dd grew out of and use it with the Safe Voyage. We have no complaints!
We have the Safe Voyage and are very happy with it. I believe it is similar in size to the Britax Marathon, but the weight limit is 55 lbs. instead of 65 lbs. (from what I remember). My son will reach the height limit well before he is 55 lbs., so I don't think that's a big issue. The Safe Voyage certainly seems to be made by Britax - the body looks the same as our Britax seat and the warranty card is returned directly to Britax. The fabric isn't quite as nice, but for $100 less, I'm not complaining!
I see you're in Upstate NY. If you're near Albany, Babyland has the Safe Voyage in stock (as of a couple weeks ago). I bought mine on-line, from www.albeebaby.com.
I've heard nothing but good things about it. It doesn't tether rearfacing, that's the only bad thing one can say about it. I think it's maybe also missing the lockoffs? But overall, a VERY nice seat for the price!
We actually just received our 2nd one today via UPS. Bought the 1st one for DS1 and he loves it! Got the red/black one (read somewhere it's not as "slippery" as the other color combo.) One of the seats we have for DS2 wasn't installing great so we ordered a second one for him.
I can't remember which site it is but one of the sites that sell them actually lists the differences between the FPSVD and Marathon.