The main problem I had with the MK4 hot end was bulging. I fixed this with a combination of three things.

I purchased a length of PTFE Round Rod (3/4" OD) which is a little larger diameter than standard and turned a new thermal barrier on my lathe. Except for the OD, all specs were the same as standard. Then during assembly I added a hose clamp. Lastly, I never insulate it. I found it tends to overheat too easily and increased the chances of bulging.

As far as clogging, it happens rarely but it used to happen more often. Unless for some reason the temperature was too low, the problem was always some foreign material that managed to get in. So cleaning it out during initial assembly and keeping the filament clean during printing are critical. I now have an enclosed feed area and use a filament guide so it's not exposed during use. Since doing this I've gone through entire 5lb rolls of filament without clogs.

Since nothing is 100%, to make life easier if it should clog I assemble the hot end with the nichrome slightly back from the nozzle and tape over it with Kapton making sure to not cover the nozzle. Then I tape the thermistor with one or 2 wraps of narrow Kapton directly to the nozzle without overlapping the nichrome taped area. In the event of a clog, I remove the thermistor, turn on the heater and put a wrench on the nozzle. As soon as it breaks loose and turns easily I turn off the heater and remove the nozzle. I put this in a small jar with some acetone and use cotton swaps and a small drill bit or piece of guitar string until it is completely clean. Then I'll usually turn the heater back on and run a metal rod through from the feed end to clear the barrel. While still hot I replace the nozzle then turn off the heater. Once cool I remount the thermistor.

One more thing, the Kapton on the nichrome can burn through. If this happens I carefully add a few more wraps. I never remove Kapton after the nichrome has gone through its initial heating. Removing it pulls insulation from the nichrome and creates a short. The only way to fix this is to do a hot end rebuild.

Sorry for the long winded response, but all the above was from experiences over many months and multiple failures. Hopefully it can help others avoid the same.