Manual lenses on Sigma SD15

I used probably the last opportunity and bought new Sigma SD15 with 18-50/2.8-4.5 lens for 350 Euro. I was lucky and this combo produces very nice sharp images.

I have M42-Sigma SA adapter and as I am in Russia there are a lot of cheap manual lenses for M42 bayonet here.

My question is:

- is it troublesome using manual focus lenses on SD15 (correct focusing and aperture settings)?

- what lenses will you recommend basing on your experience?

I will be appreciate your advice.

Thank you,

Vladimir