I also did mine with Medcert as my GP would not provide one due to "practice policy".Medcert are £60 for those whose GP is reluctant to complete the pro forma document. If your GP is cheaper then great but it sets a good ceiling price.
If your GP charges more than Medcert, then use Medcert.
I had to nudge Medcert a couple of times for some reason (despite obtaining my medical records and sending them to Medcert myself), but they were much more efficient when a shooting friend used them soon afterwards (and that includes the sourcing his records). So, I'd say it's worth chivvying them along if time is an issue as they can do it quickly!
Edited to add: my GP provided my records FoC, but practice policy prevented him completing the police form. I sent in the records to the FLO with a covering letter, and they were sent back 2 weeks later with a note insisting a completed form was required. At which point I contacted Medcert.
