Aye, the mod is brilliant. While the game engine can't model certain things perfectly, Beery seems to find near-perfect "abstractions" that make everything "feel right" within tech limits.
Of course, you have to use your imagination, as you must do in all sims to have fun. I don't mean you should eat canned food and moldy bread during no TC patrols or get under the shower dressed everytime you climb up the tower in a storm, but you do need to put yourself in your crew's suits every now and then to see why they react in this or this other way.
I am playing my current career with RUb 1.4.2 and I'm on my fifth patrol with my recently acquired IXb. Indeed, the fatigue model seemed odd at first, but it wasn't as absurd as putting the crew to bed and reading fairy tales to them every four hours, so I gave it a shot.
Patrol after patrol, the crew gets better, but even in the first patrol their behaviour was "reasonable". As real U-Boot captains probably did, I tend to stick to my patrol grid and investigate nearby convoy lanes for a day or two, but never ignore my orders and travel freely to "my favourite hunting ground" to run reckless patrols just for the hell of it. In these runs, my crew performed admirably: straight route at ahead 1/3 towards my patrol area, 24 hours there, 24 to 48 hours checking a nearby convoy lane on my way back. If I haven't found anything by then I just call it a day. Only once have I entered a port, and it was Dover, which is open enough not to be considered a port
It was at night and during a storm, so I thought it was "fair". Plus, it was on my route to the patrol area.
Of course, if I went to, say, BF29 for a patrol, then spent four weeks hunting down convoys, then checked Loch Ewe and then endured a one-day fight with all the escorts Britain can send my way, my crew would have gone nuts and become highly inefficient.
In short, RUb 1.4.2's fatigue model makes it so fatigue is "not an issue" in a "normal" U-Boot patrol, and a very serious factor if you want to go "beyond the call of duty" and win the war yourself.
Quite on spot if you ask me.
Now if that deck gun felt half as right...