1. The only purpose of a beta id for you to find problems and report them, it's NOT so you can get Q before everyone else does. If you're not going to report problems, if you don't want problems, don't bother. Even Beta 5 may have problems. Even the final release may have problems. That's what Android is for. If you just want a phone that works out of the box and keeps updating, get an iPhone.
As for the conversion back to Pie, there's one slight, but definite, possibility, and that's hard-bricking the phone. It's rare, but it happens. Google is aware of it - and the fix for it - but the customer service people aren't, and you may end up woithout a phone until they send you the replacement. (Or, if it happens [you'll be in the bootloader with no way out, and the phone won't be recognized by a PC, so make sure the bootloader is unlocked in Developer options*. Then hold the power button in [the bootloader screen will keep flashing on and off] until the phone vibrates. Then it should be recognized by the PC, and you can just fastboot boot boot.img [get the file from the latest Pie factory update] if you want to see if your files are still there [they should be], then fastboot flash boot boot.img to get the phone back. [And if you'd installed Magisk, TWRP or both, you'll have to do it again.])
The hard brick appears to only affect the booting ability of the phone - it can't boot Android, it can't boot recovery, so it boots the bootloader.
Also be aware - some apps (many apps, in fact) haven't been updated to Q yet, so you may have to do without them until after Q is released and they get updated (which is why I left the Beta program - the phone was useless to me without a few apps that wouldn't run) - and why my phone got bricked.
*Unlocking the bootloader does a factory reset, so make sure you have backups of everything first. Locally. Just in case. And if you haven't updated by PC at least once, I really wouldn't go into the Beta program. You might find yourself doing that as often as you make phone calls at some point. You want it to be second nature.