This unit allows your Garmin to be firmly fixed to your bike.
As far as the memory card eTrex devices goes, I do have a memory card device and, yes, it does work. The ony proviso is that the back supplied with kit will not fit your device, but when you bought the GPS in the first place, there will have been a screw in bracket included.
Basic comment if you have a memory eTrex is: if you still have the mount that came with your GPS, this will work; if you don't, then it will not work.
If you have lost the clips that came with your eTrex unit, the part number for a replacement is 145-00709-00. Mine has just broken and I'm trying to find a replacement. I'll 'phone Garmin when they're open and see if they can help me.
Well, excellent customer service from Garmin. I telephoned them and, after a few menu selections to get to the right department, I spoke to one of their support people. He said, "the bad news is that it isn't an accessory listed for you to buy. The good news is, since you can't buy it, I'll drop one in the post today free of charge".
I couldn't have asked for better service from Garmin.
It's dealings like that which make me think that, when I do eventually replace the unit, I'll probably buy another Garmin...