Hi Juha,
>Now we can state our points as many times you want [...]
Oh, I'd say we didn't really disagree about the factual points we both posted. (I accept the list of disadvantages you listed, and I take it that by posting that list instead of disagreeing with the advantages I listed, you accept my points too.) It's only in the conclusion we disagreed - I consider the MK 108 an excellent dogfighting weapon, and you (as I interpreted it

don't.
>1) low muzzle velocity made hitting harder because it means longer flight time and so made the estimation of correct lead more difficult.
At short range, with a centre-line mounted low-dispersion weapon, this is not that much of a problem. The technique is to aim ahead of the fuselage without attempting to track perfectly, and fire a burst of just a few rounds. The spread of the burst has a good chance of overlapping the length of the fuselage if you do this correctly.
This is only a worthwhile tactic because of the high firepower of the weapon, meaning that you only need one or two hits to bring down the target. With a lower-firepower weapon, it would take multiple hits, and you can only get in a few hits per pass this way.
(It's a highly attractive tactic due to the out-of-plane, high-energy, non-tracking fighting style implications I mentioned above. Due to the preference of intersecting vectors over pursuit curves, it also decreases the average firing ranges, which is a desired effect.)
>2) Low muzzle velocity means it was very preferable to open fire at short distance but the very effective ammo was itself problem here because it greatly increased risks of the shooter being hit by debris from target.
Oh, but how many Luftwaffe aircraft were actually lost to that? I don't think it was much of an operational concern and paled in comparison to the advantages of the high firepower the MK 108 offered. With regard to Major Jabs, I haven't read the report you mention (but of course would be interested to, if you have a link), but I think he was flying as a night fighter in 1944, so I guess he wasn't actually dogfighting enemy fighters, but rather blowing up bomb-loaden Viermots at point-blank range.
Additionally, using the snapshot tactics I mentioned means that you are not usually flying in the wake of your target where the debris would strike you. A disintegrating aircraft isn't equivalent to a fragmentation warhead, but the parts coming off are decelerated by the increased drag (and lack of propulsion) of the debris compared to the attacking aircraft, becoming sort of a stationary obstacle a pursuing attacking flies into. If you're not pursuing, there is not much danger.
>3) Memories of at least a few aces mentioned the tendency of MK 108 jam if fired under G-forces much different from 1.
Again, how often did this happen? All weapons suffered from a certain jam rate, with G forces playing a role for pretty much any weapon ... and anecdotal evidence is not very good for determining the actual operational impact of anything.
(By the way, the snapshot tactic I described actually tends to minimize the G rates pulled while firing because it's not necessary - or desired - to actually track the target. Some Gs might still be pulled, though.)
Regards,
Henning (HoHun)