When one could just read, practice, and spend the money on a cavern/intro cave course? Plusses and minuses?? Why not enjoy the cavern, and not worry about another C card.
On the assumption that this is a serious question:
Do you actually understand what GUE-F is? It certainly isn't a cavern course that's for sure - so comparing the two is a bit difficult.
If you want to do some relatively straightforward cavern dives, there may be little advantage in doing GUE-F... provided you pick a good cavern instructor.
GUE-F, as I understand it, really just exists because people entering Tech 1 and Cave 1 didn't have the comfort level in fundamental skills to enable them to perform them in a situation with higher task loading.
So why do GUE-F? Well, you might learn something and it might help you become a better diver. Then again, it might not. I'd alrady done a number of TDI courses and done a lot of extended wreck penetration dives well beyond the limits of recreational wreck diving. I found GUE-F to be good value for money - the ncie thing with the course is that there seems to be flexibility in the course standards that allows the instructor to push capable students that little bit further. The two of us on my course were in a similar situation of having done TDI courses and being reasonably competent at the "fundies" skills - so the instructor ended up introducing new skill combinations and pushed us to the point where we realised our own limitations. If you've already got good buoyancy, trim and control then you'll get pushed just as far.
As far as I am concerned, there are no disadvantages to doing GUE-F, no matter what you want to do afterwards. You may get the same level of focus on trim and buoyancy from good cavern or cave instructors from other agencies - but then again, you may not.
What I enjoyed the most was the attitude of the instructor - whether or not something is "DIR compliant" is quite frankly a load of horse****. We had some good discussions about why the preferred system is the way it is. Some of it I disagree with, but I can certainly see the reasons for it. There was no pressure at all to adopt a particular element of it - it was very much about informing divers of the reasons for something and getting them to think about what they are doing and why. I mean, goodness, we did our dives on air during the course - whereas if you beleive what you read on the internet (I am a dog, by the way... woof) then such an abomination should never be allowed to happen. GUE are a lot lighter hearted than you'd think.
Oh, on the "seacure mouthpiece not being DIR compliant"... again, probably horse****. But think about why that might have been someones response - it's pretty much standardised now in technical diving that in an OOG you donate the regulator from your mouth. Using a mouthpiece that only fits your mouth is just downright unfair - I had the same thing abut not using seacure mouthpieces from my TDI instructor a long time ago.
Another comment on the "GUE=DIR" thing. Again more horse****. GUE are actively moving away from the phrase "Doing it Right", hence the change of name from DIR-F to GUE-F. The way I understand it is that the vast majority of DIR divers never actually leave their computers, but seem to know everything about DIR. The internet-DIR divers may be rigid and inflexible, but that's certainly nothing near the truth when it comes to GUE instructors.