50% Update. No problem with getting the TPU to stick to the structured PEI print bed. 2 of 3 objects done. Obviously far more stringing compared to PLA or PETG, but not a big problem IMHO, can be fixed after print has finished. After the print finished I heated the bed to 70°C and removing the parts was no problem. And no damage to the PEI plate, AFAICS. Now printing two lens covers with TPU.