I just tested the app for the first time (Magic player since the late 90s, played Arena during beta) and wanted to give some suggestions.

• the app then redirected me to this website
• where I had to log in
• I then typed a collection of suggestions in one post because there was no way in heck I was going to go through this multiple times
• and to top it off, the "post idea" button didn't work (latest Chrome on Android), so I couldn't submit my post. (edit: this may have been due to the screenshot I was attempting to attach being a PNG file, in which case, please add an easily visible error message instead of just making me tap the "post idea" button until I get sick of it and move to my PC)

Currently writing this on my laptop, where at least, it's easier to make multiple quick posts.

Seriously though, please just give us the option to quickly type feedback in the app and hit "send". Otherwise, the barrier to providing feedback is just too high, plus, people will be more likely to wait until they close the client (and then forget about it).

If you're worried about the flood of duplicate posts, come up with a simple tag system.

EDIT: I think I'm now on a general Arena feedback site and I'm not sure how to get to a specialized mobile one, so I'm just leaving this here. Supports my point pretty well, though, and having the same option on PC wouldn't hurt anyway...