My old Silca pump head had the plain black EPDM gasket and was worn out and slipping off of the presta valves I tried to fill. I put this new one in the old head and it fit the pump head and presta valves perfectly. (I have the large diameter presta only head, not the reversible prestaschrader type) I have only filled a dozen tires so far but the performance so far has been faultless. I can't say how long it will last yet but seems like good material. The price was kind of high for a little bit of rubber but the BTD price was as good as anyone else and the delivery was fast.
This rating is probably confused with a general rating of Silca pumps. The design of Silca products allows for replacement of any parts as they wear to extend the lifetime of the pumps. This design has kept my Silca going for 22 years. This gasket is probably the tenth in that time. The pump sees very regular use. Daily and often by multiple users at club rides.
Didn't seal. Gage needle dropped as quickly as the pressure stroke raised it. Went back to large rubber washer, which worked just fine. Maybe I didn't give it enough chance, but if it's still in the junk parts box when I'm out of rubber washers I'll try it again.