I found the GelKam, (fruit flavour), to make my teeth sting. I presume it's not pH neutral. You may not have this issue, but if you do, you're not alone. My favourite fluoride gel product is the PCXX made in Canada (I've only used the no-flavour version and recommend it). This page includes a list of Canadian and US distributors. It is not a prescription item in Canada, but I don't know if any of these distributors will ship overseas, or at what cost:

http://www.epsross.com/PCxx.entry.htm

It's a great product, though.

I'm in London, England now and haven't managed to find a way to get this, but I've since been prescribed a different product here (which I haven't tried yet).

Good luck.

-Seth

47 yr old male non-smoker, social drinker, fit. Jan'10, Stg3 rt tonsil+rt neck SCC, HPV+, rad+chmo Vancouver Cda. 2yr clear Apr'12 London UK. Apr'13 mets recur to lymph btw left lung & aorta, 3x Cisplatin+5FUchemo+20 rad, was all clear but 6-mo PET-CT shows mets to pleura around left lung, participating in St 1 trial of GDC-0980. GDC lost effect and ended July'14, bad atrial fibrillation requiring hospitalisation, start more standard chemo 10 Sep 2014.
Sadly has passed away, notified Jan 2015.