You may find something here : freaktab.com/forum/tv-player-support/amlogic-based-tv-players/s805/others-ab/550512-mxq-am_mxq_a-firmware just make sure you get the correct system specs version.
Also here : blog.geekbuying.com/2016/05/mxq-4k-rk3229-smart-tv-box-android-5-1-firmware-update-20160526/?admitad_uid=e3069f3745808505912f664203fbd4b1&utm_source=admitad not sure if its the same though.
Yeah I have flashed many TV Box's and they work great. You just have to do it the right way and use the right image for that model and it should be OK. Compton, don't worry if you mess up your TV Box, I can send you one for free.