The main issue with a mechanical locker and winter driving is ice, as it can make for sketchy driving. With standard 4wd you have opposing wheels driving the vehicle, this balances out traction and keeps the rear from wanting to switch places with the front. With a mechanical locker in the rear, this balance is upset, and you have to account for it when driving. For some this isn't an issue, and say it is easy to compensate, others I know have swapped out their mechanical or spool, after the first time the rear end tried to come around them on ice.
Yes, mechanical lockers are cheaper and easier to install, but an ARB locker should only cost you an hour of bench labor for a shop to install it in your 3rd member. Also, you do recoup the additional costs overtime with less tire wear, especially with a rig that is driven daily as a commuter vehicle.
Something else to consider is, do you really need a locker at this time, or for the type of trails you run, would a winch be more beneficial?
Unfortunately I have seen a solenoid fail on the trail at a MCRoundup. The guy had a CO2 tank and it drained his tank and he couldn't operate either diff after that. It does seems like a rare occurrence