I have tried Speedify (not with such an impressive setup) on multiple 4g connections (different towers, different providers) and didn't see much, or indeed any, throughput bump. So I sort of gave up, because ~20mbps is surprisingly livable-with. I would definitely be interested in trying again, especially with a starlink + 4g + crap-uk-rural-adsl.
I did also once have to manage one of those Mushroom bonding things and....never again, please.