Pre-lockdown/ remote working, I was using the Minoura FG540 Magnetic Hybrid Roller.
TR doesn’t offer virtual power for it, but if you have a power meter… It was significantly cheaper than the Omnium at the time (actually the difference would’ve covered most of the cost of a 4iii). Can’t help regarding 1x/ sub compact, but I haven’t come close to maxing out on a road compact, including sprints/ bursts!
Haven’t seen the omnium to compare sizes, but I have the Minoura in a gym bag.