I previously sold the XL4 at my old shop.
This is a bit of an outlier as our shop was in *extremely cold* water (read, -2 to 4*C 6 months of the year), but the XL4 reg sets did not stand up to the same cold tolerance that the rest of the apeks lineup was capable of. This was no matter how new or tuned they were, nor if we put new kits into them. A new 2nd stage diaphragm helped slightly, but overall they were much more prone to cold-induced free flows. Interestingly, a chat with Aqualung made it seem like these were initially designed to be deco regs.
FYI, the only difference (as far as I remember) between the XL4 and the XL4+ is an additional HP port, so don't let the + fool you into better performance or something.
As far as the Deep6 goes, the regs are well priced and appear to be well recieved by the community.
Being able to service yourself is nice, but again I do recommend having some training as often things go deeper than swapping o-rings, and I have seen too many scratched regs from non-suitable tools being used, which cause leaks or IP creeps. One of the downsides I do see with Deep6 is the chroming is thinner than some other regs. This also makes me a little concerned about the 2nd stage plastics. I have personally seen a few brands of regs commonly fail when cold and dropped (Sorry DiveRite).
IF you are good at washing your gear and are somewhat gentle with your regs this shouldn't be a problem.
Honestly though, what does your local shop sell and service?
Most issues with gear arise as you are about to use it, and its nice to pop down to a local shop to get them fixed. I can see that being an issue with Deep6, whether you need to send it back or they need to send you a part. Your local shop will more likely appreciate you buying the regs from them and will likely give you a rental reg (or they should) while they hold onto yours to be fixed.