I'm a huge Helios fan, and have two copies of the 44 M. One copy has the aperture pin removed and the other is completely standard.
The lenses are very well made, the build quality is as good as the Takumars I have and they have a very nice tactile feel to them.
If the focusing ring isn't stiff they are silky smooth.
A stiff focusing ring can be easily fixed, there are detailed instructions all around the internet.
The other commonly reported problem is oil on the aperture blades, which if very bad can cause the blades to stick. But light oil doesn't seem to have any detrimental effect.
Modifying or removing the aperture pin is a popular modification that disables the AUTO -MANUAL switch and makes the aperture ring available in both positions.
Without the modification the switch allows the aperture to be quickly opened up when focusing and then stopped back down to the preset aperture. I find that I'm using the unmodified lens all the time now as I think it's easier.
I haven't got the technical knowledge to comment on the optics of thelens, but as a regular user of the Helios I rarely have cause to critisize the results, I get sharp and accurately coloured pictures from this easy to use lens.
It benefits from a lens hood to reduce flare, but it's not a huge problem.
I still see this lens for sale at less than ÂŁ10 in the UK, which is a remarkable price for such a great lens, personally I think it's a legendary lens because of the combination of quality and price.
There's no reason to not have one.