Hiya mate,
first off I note he doesnt advertise the ptfe heads now on his web site- but does seem to mention them in the tune kits he does (so not sure if he makes them anymore)- best ring and check.

As for whether to get one for your Merc- well I can only say I've fitted them to Dianas, Anschutz, (about 5 or 6 rifles now- cant recall) and with the exception of a HW35 I also did they have worked very well, and given improvments in both consistency and power (be careful with the latter though). Not sure if the Merc is a model covered in the range he does/used to produce?

Best regards,
Dave