Although I'm not in the market for one of these devices, I'd be careful about warranty and return, so you should try to pay with Paypal, who offer some measure of buyer protection.
Checking #1 I notice 4 x 45 w output. There is a huge difference between 45w RMS (best) and 45w PMP (poor). That needs to be checked. Note, if it's 45w RMS, then the machine is going to have to be able to dissipate a fair amount of heat, have you considered this and is there adequate ventilation for long term reliable performance.
They all look fancy, but how well do they actually perform. Have you not checked audio retailers so you can hear the sound for yourself.
There's GPS and there's GPS, some are much better than others, but buying this way, you won't know until it's installed how up to date the maps are and how well it works.
Good luck with your search, but if I were making a purchase, it would be from a local store that I could annoy in the event of "difficulties", just saying.
