Please note my highest GUE qualification is REC 3. My highest non-GUE qualification is IANTD ART, so i'm just a diver who straddles the line between rec and tech.
One of the biggest differences I have found is there are a lot more maths involved in other agencies besides GUE, in regards to working out CNS percentages. GUE have a simple maths calculation to figure out CNS percentages on dives, whereas IANTD have a chart where you have to figure time, PPO2s, etc at various depths and stops, then you add it all together. It's quite a lengthy process.
GUE obviously teach standard gases. If you are diving to a max of x depth, you use x gas. IANTD teach best mix. Personally, I am a fan of standard gases. Valve drill/shutdown procedures are different. GUE= go for the affected post. Once the offending post is shutdown, call the team in to take a look, see if it's fixable/non-fixable and make a decision on whether or not to continue the dive. IANTD=isolator first, save at least half your gas and basically call the dive. GUE's gas switching procedure is a more thorough, longer process, but both courses had team verification before a switch happened.
There were more failures in Rec 3, than there were in ART. Actually ART didn't have any failures, but shutdowns were done on each and every dive. Rec 3 was simple failures and no where near what happens at the tech 1 level. We also had primary light failures, back-up light deployments, spare mask deployments on rec 3. On ART we had a 15m no mask swim followed by an OOG/s-drill, plus a swimming air share. Both courses had loads of s-drills, OOGs, blob deployments, etc. ART also had the highly stressful skill of remove and replace your twinset underwater. That was not fun.
Ascent work was done on both courses as well. But rec 3 had more ascents, as well as varied ascent speeds (9m/min, 6m/min, 3m/min, 1m/min) vs 9m/min on ART. Both courses had us calculate SAC rate, but on rec 3, we were taught how to use our sac rate to guesstimate how long of a dive we would have. Checking our spgs was basically double checking our brain if that makes sense. With GUE, minimum gas is obviously the main gas rule, with either all useable, half or thirds. IANTD was thirds only, with the final third being what we started the ascent at (as opposed to minimum gas).
Rec 3 was a 5 day course, with a total of 9 dives (6 critical skills, 3 experience dives), and 12-15 hours in the water (to be fair, it was August in Croatia). We also went to the max limit of the qualification for the experience dives (40m). IANTD was 4 days with a total of 6 dives (4 critical skills, 2 experience dives), with about 6-8 hours in the water (in February in the UK in a quarry). However, we only hit a max depth of 40m on the experience dives (qualifies to 48m). Both courses stressed the importance of working together as a team. Both courses also went above and beyond the bare minimum requirements, and neither was a definite pass. I feel that rec 3 was a more thorough course skills wise compared to ART (but both were very good courses), but ART actually qualifies me for a higher level of diving (48m with up to 100% o2 for 15 minutes of deco vs 40m with 32% deco max 15 minutes for rec 3).
Personally, I took both courses for very different reasons. Rec 3 opens up a whole load of diving in the UK with a sensible gas choice, while still allowing me to dive within the GUE community. To be honest, when it comes to sea diving, I am quite happy diving to the limits that rec 3 offers me. It is south coast UK diving. The main reason I took ART was to enable me to assist/safety dive/DM on the course at the dive centre I work for. Even though on the course, they do not go below 40m, I still need be certified to 48m for insurance reasons. The skill set on both courses is similar, but there are differences in procedures, a few skills, etc.
