Ok, I tested them again yesterday in a session. Unfortunately I didn't have time to do more, but I managed to set up a comparison of spaced pair of KSM141 in omni and CM3 in the same position above the balafon on the same take with the same preamps - some average (but very OK) preamps in Yamaha AW1600 recorder.
I like the tone of CM3, but they do exaggerate the extended low bass vibrations - the chart for KSM141 in omni extend well down below very linear, too, but there is none of that rumble to be heard. But that's nothing a low cut of some 18dB at around 85Hz couldn't solve, though. Still I am curious why is that? I don't buy into the argument that they go down in a more linear way than other mics - for example here's the omni frequency response of KSM141 (the second chart)
There's even a visible sub bass lift and still no rumble heard in omni setting.
Anyway - I like the tone of CM3 and I would use them instead of KSM141 on balafon, but since I was afraid to screw the session with the mic I don't know well enough, yet, I couldn't use them this time. Solving the problem with low cut didn't seem right to me, since there was no problem with other mics... I was afraid something is wrong with the mic.
I'll keep them, because for the price they are good. But I have a clearer picture of what they are now. They are a 230EUR (per pair) mic with a nice tone, but not "killer of Schoeps" or anything of that sort. Also if a friend would ask me what to take (as the only mic pair) on a recording field trip to Guinea I wouldn't recommend that mic, since it doesn't seem to be so reliable in ALL the situations... Something like a KSM141 seems to be more of a reliable workhorse. Or maybe a pair of RODE NT55. But they are almost twice the price of CM3. And I expect a pair of Schoeps MK21 would deliver that wide cardioid "mojo" and the tone comparable to CM3 (or maybe a bit clearer?) with no compromises and a feeling of reliability and "no fuss".
So for now, I'll stick to them. I think it is more that I like the characteristics of wide cardioid - a blend of cardioid focus and more natural picture of omni. So, my wet dream is not solved. Still have to save for a pair of Schoeps MK21... (so - for masturbatory purposes - if anyone can post more direct comparisons between Schoeps MK21 and Line Audio CM3 in different settings and on different instruments would be welcome).