Welcome to the SeeMeCNC Community

I'm using FSR (Thanks to mhackney and his awesome blog) with a 0.8mm PEI sheet. There has been no issue regarding heat so far.

Tested up to 260c on the head and 110c on the bed without issue.

The only slight downside is the small trace of plastic from the nozzle touching the bed at each point; if not cleaned between passes the residue will interfere with the leveling.

So far the move to Duet with FSR is the single best upgrade I've made to the Max, and i highly recommend anyone make the swap.
Also upgraded to PEI (obviously) and an E3D v6, along with some electronics and cooling tweaks.

My PEI is on it's route, but I can already concur with your view on the Duet and FSR upgrade. It is true that probably the hot-calibration is always a bit off because off the oozing at the probe points. That makes it difficult to embed the calibration into the startscript of a print, because you need time to clean the bed first.