Regarding all the well-intended comments on M26 connections: yes, that's what it says in the regulation. Nobody I know, in any European country, follows this. Neither the divers, nor the instructors, nor the dive shops. Do not buy M26 regulators, you pay a premium that is pointless. In many places it will be hard to get cylinders or fills. There may be some small exceptions, but really, I do not know anyone who uses M26.
And btw, if you meet a die-hard that tells you, that you need M26 for Nitrox, try this: ask them which connection is the EU standard for Trimix (say 21/35). They will inform you it's M25. Now carefully think how you fill Trimix. Yes, that's right, you add pure oxygen before topping off with air (or banked Nitrox). Thus, by definition, it is ok to fill pure O2 into M25 bottles ...
If you get a real nitpicker in a dive shop, telling you, you cant have Nitrox in an M25 cyclinder, then tell them you want Nitrox 32/1 or 50/1 or whatever and have fun watching them fill it ...
Also no offense intended to the many well meaning comments from across the pond, but sometimes it's important to actually know the local reality when giving advice.