Hi
I use the T-locks most of the time, especially when there is pronounced film curl, which the T-locks tame very well. However, some film stocks seem to sag downwards no matter which way you mount them. In these instances, it pays to tape them to a piece of ANR glass. You do need to keep the glass very clean and dust-free though.
I always use betterscanning.com glass on the rare occasions I scan 35mm with the Epson. I also have a custom-cut piece for the OEM 120 holder. (I don't know if the betterscanning glass fits the Epson 120 holder.) Obviously, in the absence of T-locks for the Epson holders, the glass gives a vastly improved scan with curled negs.
Peter