Yeah, I used to use LoFi ATC, but it stopped working. Built something to scratch the itch: https://tonygaeta.com/labs/atc-lofi. OP’s design is solid—great site with good options.
Don't get me wrong, but I think this is a perfectly good place for a feedback, since you made the Show HN post. There is no need to redirect users to Google Forms.
It was actually more a technical question, the site uses LiveATC streams, there doesn't seem to be any specific reason to limit which stream the user chooses, I was just wondering if there was any particular reason for it. Maybe you could include an 'advanced' section where users can enter their own stream code (e.g. not 'ksfo_twr' but 'lhbp_app2' or whatever?