I don't think you can go wrong with that choice of the PD-M540
I've been looking to replace IC4 stock pedals too but my wife may decide to start riding so I'll probably look at dual sided pedals. Currently considering these two SPD MTB oriented models
https://www.amazon.com/Shimano-PD-T8000-Trekking-Bicycle-Clipless/dp/B01HI6M1KU/
OR
https://www.amazon.com/SHIMANO-PD-EH500-Pedals-Included-Platform/dp/B07FTB9MCW/
Not sure what you're looking at in terms of ' sellers insist not to use mountain bike SPD pedals on indoor training bicycles'. SPD are just fine for indoor bikes. You don't need top of the line road pedals and the stiffest carbon fiber soled shoes for an indoor bike unless you're a serious competition rider looking for max power transfer in your workouts and then you're more likely to have a road bike set up on an indoor smart trainer. You also don't need to break the bank on the lightest pedals because ... you're not going anywhere on the stationary bike so weight isn't a big deal ;-)