I'm late to the party, but I've been running MC 6Pak shocks for almost 4 years now. My 35" tires regularly get stuffed and these shocks have performed very well for my requirement, i.e. to do a short arm bolt on build that would give me the max flex. Truth be told, it wasn't a true "bolt on", because the rear shocks required removing the lower mounts and welding in the MC mounts. That said, I viewed that modification in the same class as replacing the stock lower control arm mounts, it was something I was willing to do.
Overall, I've been very pleased with them. The fronts give me more flex than my previous two shock setups and the ride is smooth. The rears were more challenging and I struggled initially with interference issues, due to the size of the shock body. The rears also require significant bump stopping, which limits their effectiveness (I'm running 3.25").
In terms of reliability, I just sent my shocks in for a their first rebuild. The cost was very reasonable and what I'd expect for any rebuidable shock. Would I buy them again? The short answer is yes. To be 100% transparent, these are not for everyone. As others have said, unless you're going to try and squeeze out every bit of performance out of stock control arm and shock mounts , and use it regularly, there are other less costly alternatives. My dream build would be a mid arm, with extended upper shock mounts, but for now I can wheel my Jeep every place I'm comfortable going and many I'm not.
The pictures below show the front with 6Paks and the rear with Bilstiens. (My rear 6 Paks were out getting rebuilt).
