[ Moderator note: please be polite and helpful to each other. ] 

There's a bit of unnecessary hyperbole here, perhaps caused by imprecise terminology due to Garmin's confusing naming scheme.

Garmin eTrex 10, the subject of this thread, is about 6 years old. (2011-05), Geocaching-aware, has a USB mini-B, shows up as a mass storage device, you copy GPX files to it. It's a reasonable, albeit low-end, device. I'd be surprised if any software that supported the post-Colorado era devices didn't support these. (GPSBabel has no special code for it; it Just Works with our GPX writer.)
  The original eTrex hails from 2000. It has a serial port and thus needs a USB-serial adapter and all the pain that goes with that to attach to any modern computer. You certainly can geocache with it, but you're going to suffer. If you already have the cables and adapters and such, you can use GPSBabel or EasyGPS to get PQs or even .loc files to it, just like you've been able to do since the early 2000's. Honestly, if you've not already made that investment, it's hard to recommend doing so.

Between these two points (2007) was the eTrex H, which was a respin of the original. It's basically the same primitive design, terrible screen, serial port, etc. but it has a better receiver chip that doesn't lose a signal if you're in tall grass. I'm guessing this product existed only because there were so many schools and books using the original and they ran into parts availability problems that they went to a maintaining engineer and said "change as little as possible, but replace the GPS chip (that we can probably no longer get)".

As for being" legacy, a mid-life booster ten years ago to a 17 year old design can distort our views, but in tech, these are quite old devices. They can be made to work in today's ecosystem, but you're going to pay with your time and frustration. They're not quite an Okidata 200 or an Epson FX-80 from Mineral's posts, but some of the issues to conquer are similar.

My general guideline is "etrex followed by a number is viable. If it has a serial port, cut your losses".
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