To be honest, I have a f5 and va3 that use the new plug in the back, and also have had a 645m for months, and I REALLY prefer the clip! For example, if you need to use garmin Express, you can do it without taking off the watch. Same for "charge on the go". I also find the clip more reliable when connecting.
I'm also happy with the clip. If I compare to Polar's Micro-USB solution at the back of the watch, I feel the clip is so much better. It always feels secure in a way that it can't get loose. Why does the clip bother you?
Not sure what the 645 Charging clip looks like but I am not a huge fan of the charging cable for the 935 the socket is prone to having water sit in it so needs blowing out to dry it. I quite like the older magnetic clip for the 610 - very positive fit easy to use and watch sat flat whilst charging
I had my doubts as well, but the clip works very good. You even have the option to charge the watch during an activity... try that with a VA3 or Fenix!