Chilli - pre-covid we moved across  to IEMs and with personal mixers,  had the best mixes  ever - BUT - at festivals it went horribly  wrong. Festival sound guys with  few exceptions are  old rock and rollers, or young people first outing  in the industry and their monitor mixes with wedges are at best average. I realise there will be some excellent guys out there, but  we  just met few of them. With wedges if your mix is totally screwed you  can usually hear enough to play - a struggle but you get  through. The commonest thing is they are so far away, they  cannot tell who you are or even what  role  in the band you have, so  can I have a bit more keys in the mix please probably gets the keys players mix changed not my bass! With IEMs it's intolerable. With them  in you really need a balanced mix and a quick line check is NOT going to work. What we did (for 5 or 6 shows before Covid was buy an X32 rack and stick it in our usual stage  rack. We rigged a festival system.  We could pre-rig our 4 vocal mic cables with a Y splitter and drum overhead plus bass, guitar and keys feed - just 8  mics/DI and we and our sound guy we always take with us could unplug their 4 vocal mics, add our splitters and replug, plus the DIs, and one boom stand we put over the kit. This gives us all our vital feeds and the stage or FOH festival people get their pre-labelled sources. My  bass  amp and the guitar amp have  DI out, and the keyboard just needs a DI box. It works really well.  It means we're totally  independent - our personal  mixers are network cables so we can get rigged quickly, ready to play because we don't need to do our mixes.
I find the IEM  mix in just one ear very difficult to play with. Festival stages  are only good with  IEMS if you have proper soundcheck time and our band have four part harmonies in every song - and in my case, if I lose the keyboard channel, I have no idea if I'm in tune. At one festival the stage level was criminal and I played one entire song in Eb, for getting we'd decided to play it in E for a change. I did the whole song wrong - but never heard a thing as I'd  pulled my ears out because the mix was so awful. I play my bass by remote control, so could  still play the right (but wrong) notes without hearing them. I only knew when the sound man told afterwards. I've even played a  gig  with the ears in and the pack off because it was so loud.