I have never done a gue course, and I don't think I will do, or it must be free. When I started diving, I was already interested in technical diving, but nobody could help me on that path. DIR was the group of divers to stay away from, you will die if you use foots on cylinders.
When I heard of gue, I was already certified for 51m with a trimix. So to start over again was no option. I started with iantd and still do that. The reason was also the price. I calculated the shortest way to 100m and that was 3 courses. For cave I started with tdi, the 1 week course from cavern to full cave. I was not rich in that time (now still not), so I could not afford me 1500 buck for a course. So I had to look for the price-path I could afford. Also I was interested in sidemount. But had no option or money to start with then.
The advanced recreational trimix was 550 euro, normoxic 450, full trimix 850 including gases(but I had looked at an more expensive option first). That was a path I could afford me. So I did. The cave was 1500 from cavern to full cave, including food, equipment, and a place to sleep and gases.
I did during my path DIR and non-DIR courses. The ART course was DIR orientated, but my normoxic was absolutely non DIR. Full trimix completely DIR again. The cave was also non DIR. Was it wrong? No, I learned to deal and to dive with every diver. The ones that are non-DIR also don't die more often. An eye opener.
My configuration is DIR. My diving is for 80% the same as is teached in gue courses. But I use sometimes ean80, half the cns of 100% on the same dive, same decotime to mention an advantage of ean80 over 100%. But I also dive solo and like solodiving and want an agency that also accepts that.
When I was ready for my full trimix course, I would have done tec-2 of gue if that was possible without first the fundies and tec1. I already could do that dives. If that was not possible, I decided to look at the cheapest way. I knew I could do that dives, so it was a waste of money to do beginner courses again.
Also I started sidemount and ccr before it was available with gue.
Okay, now why I still look at gue (and also nacd, nss-cds, naui, ssi, swedtech, ise, etc): I also teach. And I like to know what others do. I read about it. So if I now have a student with a gue base that goes further with another agency with me, I know what is learned. And what I can expect. I also can change the way of teaching. If someone wants to use standardgases, I can do, I only have to explain why best mix is also an option. But at the end, a safe diveplan must be made. I always use the END max 30m as example. DIR say END max 30m and standardgases, then it is always right. True. But for 56m depth you can use an 18/45. END at that depth 20m. So right within the DIR requirements. But you can safe 20-25 euro a dive without doing anything worse with safety and you still don't have to change your diveplan. Take an 18/35. END 28m, deco is 1-2 minutes shorter (so the 18/45 plan can be used or ratio deco, or deco on the fly).
Also you can stay most times 1 minutes longer on a wreck at 60m with an ean40 (40/15) as first decogas instead of an ean50. Just because you change deeper and can use that gas in twinset to stay 1 minute longer on the wreck and still use the 1/3rd rule.
Nice examples to be a thinking diver. So for me reading about other agencies is good to be a better instructor and not only know what you have to teach.
In the last 12 years you see gue moving more to other agencies. The bottomtimer and ratio deco and deco on the fly is now a computer, planningsoftware and pragmatic deco. I learned 10 years ago already pragmatic deco. The ratio deco can still be used as a first idea of diveplan. You directly know if people talk ******** or that they know what they are talking about. It is not 5 minutes more or less deco to be safe or not safe. Deco is still not absolute mathematics or knowledge. But with gradient factors you can adjust a plan more to fit yourself or your team than just stick to ratio deco as only truth. 20 minutes bottomtime of a 1:2 ratio doesn't mean that with 20 minutes bottomtime 42 minutes deco is wrong or that you will die with 38 minutes. But you know your plan must be around that ratio. If you want to be more conservative, you will do 45-50 minutes deco. Nothing wrong with that.
Sidemount is introduced a few years ago. Other agencies already teached sidemount for a long time. Also the same with ccr. The biggest difference is that you can start with ccr directly if you want with other agencies instead of first doing tec1 and/or tec2. Same with sidemount, you can do a full cave course in sidemount.
The ratio deco of ise is a little bit different from gue or swedtech. DIscussions about ean50 above or under the 100% are seen between agencies. But both have an argument to do it the way they do it.
So for me the reason to follow other agencies is to know what they teach. And maybe I will learn something about the theory. The diving is not different, a twinset is a twinset, a cavecookie is a cavecookie. 1/3rd is 1/3rd. END is END (only oxygen narcotic or not). Analysing and planning is for every dive needed.
And at the end, there are no statistics that 1 agency does it better with accidents than another one.
Also DIR divers follow other agencies. Just to know what is going on there. (and some to know how 'wrong' others are). Following others is human and i believe divers are also human