I had about 20 Extrema Ratios in my life so far. Am I a fan? Sure. They are one of my favorite brands. Do I like everything they make? No. Do I understand why people don't like them at all? Yes.
Extrema Ratio IMHO is very unique. Their handle design has become a signature feature only comparable to Benchmade's Axis Lock or the Spydiehole. But I also mean that they are
-Italian but not from Maniago
-100% tactical but also offer traditional and cooking knives
-rather expensive while seeming very basic
-known to be very good at hardening and working with high end and exotic steels but only use N690 in 99% of their knives (100% of their non-exclusive knives)
-overall quite controversial
The knife company that best compares to it is Emerson IMHO. They also sell knives with materials considered sub par and they also seem to be hit or miss. You either love them or you hate them. Both companies also seem to have a huge fan base in the military and law enforcement.
As stated before, I consider myself a fan but I don't like everything they make. This is mostly due to personal preference: I don't need (tacitcal) fixed blades and I don't like overbuild folders that much. What's left of Extrema Ratio's portfolio is the BF-Line and IMHO these knives are great. For me the BF2 is the only European tactical folding knife that truly is an icon. Not quite a Benchmade 940, Spyderco Para 2, Emerson CQCB-7 or Kershaw Skyline - but not too far from these either.
Are they objectively great? Probably not but it depends on where you come from and what you expect. If you want to have high end steels, titan handles and butter smooth opening you are better off buying the knife of another manufacturer. If you want a sturdy knife with a full metal handle, durable coating, a good blade geometry, an unique and easy to engage secondary locking system and a very deep carry pocket clip and can live with N690 (it is a very rust resistant good steel after all!), Teflon washers and the price then go for it! The same goes for every knife of the BF-Line and the BD4-Line (the BF4 line was renamed).
Regarding the "-R" Razor opening: I have tried it and bought a BF2-R instantly. It is a fun and unique way to open a knife! But I won't say that it is better than a traditional opening pin. It makes the knife longer in closed state and even though there is the detent that should prevent accidental opening it could probably happen. The only extra functionality you gain over a opening pin apart from extra coolness AFAIK is that you can use the knife like a kubotan or glass breaker in closed state.
tl;dr: It seems that you dig the BF(BD)4-R. If you want it then get it. It's a good knife.
I have a few, but my main carry is the MF1 BC that I got at Blade Show West. It's built like a tank, takes an edge and feels great in the hand for usage. This pretty much kicked my ZTs Emersons and Microtechs out of my rotation.
N690 takes a wicked edge! I have no complaints. Some of their knives are interesting, while others not so much. I've heard reviews both yeah and neah. If it appeals to you, have at it. Your opinion would be most welcome in the review threads here!!!
Besides the looks, I have handled a couple knives in a local store and I don't quite like them. The quality is there but the ratio of usable blade VS weight&bulk does not do it for me. I could get to love one of the most basic ligther models but that's about it.
A BF2CDs? If so than it's funny that you post under Mikel_24 who is complaining about the bad usable blade to knife ratio.
I somehow really like the BF2CDs. They have been out of production since years and have become pretty rare. What's cool about them though is that they have this tiny but still good usable blade while offering a full size grip.