That ain't their arrogance. Their arrogance is declaring all browsers other than the single one they tested to be "unsupported" and not even worth attempting to use with the app. It's one thing to warn against untested browsers; it's another thing to outright prohibit them and kick you back out to the homepage (after collecting my email address with which to spam me, no less).

If it's more a matter of some specific thing(s) that Chrome has implemented and other browsers haven't, then it'd be nice to be upfront about what that thing is so that those of us on non-Chrome browsers can bug e.g. Mozilla and Apple about it - and it would further be nice to actually test against the existence of that thing rather than gatekeeping the user agent string like it's 1999.