For glider training you want the smallest, lightest unit you can find. For

I agree to a point - I wouldn't want anything smaller than the A6. I
have the original Icom A20 that I bought over 20 years ago. Durn thing
is built like the proverbial tank and just won't quit - and it gets used
too. The problem for me was that it's the size of a brick and that's a
problem when you're climbing in and out of the back seat of a glider all
day. So, even though the A20 worked perfectly, I bought the A6 simply
because of its size. It's a great radio but I come to the field with 2
battery packs. The A20 batteries would last all day.

Tony V.