For me personally GPS function is useless, so you have to think realistically if you going to use it, how often etc. Having gps antenna plugged in every day, if you want to remove dash cam few time per day from you car for security reason not get stolen, then gps antenna is hassle every time to plug in / remove and then again attach. I find it annoying. In this case I prefer to go with built in gps, but those dash cams are different price range.
However if you decide to go with gt550w, I recommend to buy from Saddle or Foxoffer, - those two vendors has been often discussed in this forum. Most active vendor with positive feedback is Foxoffer.
yes, their price is slightly higher, but you paying for good aftersales support.