The 645 is now discontinued by Garmin. It was the first watch out of the new generation so will likely be the first one replaced when the new watches (forerunner 55, 255, 655, 755, 955, fenix 7 etc) start coming out this year. Compared to the 245, the 645 has a barometric altimeter, Garmin running power, Garmin Pay and a metel bezel. It's a bit heavier and more "premium" than the 245 but has many of the same features. It also has the older GPS chip which is less power efficient but supposedly more accurate.Alright Chaps, I've got a Garmin Vivoactive (the first one) and been tempting to upgrade it for a bit. I have noticed on Wiggle they have the 645 music. Any thoughts on this one? It is cheaper than the 245 yet has music and garmin pay so seems better.
For the £200 wiggle have the 645 on offer for, it's a great deal. Garmin support and update old devices for years so you won't have an issue there. It will likely be replaced by the 655 in a month or so but that will be nearer £400 when it's released.