I've mostly been using D'Addario Pro Steels for a long time, but when I saw that Thomann released these I bought a couple of packs to try out.
The first thing I noticed when changing from stainless steel strings back to nickel plated is the obvious change in feel and tone. Stainless steel strings are a bit brighter sounding and also has a bit rougher texture. If you prefer this or not mostly comes down to taste. I don't care much either way, but one thing that is better with stainless steel strings is that they tend to last longer, keeping that fresh and bright sounding tone. A good set of nickel plated strings can last long as well, but it depends on how well the nickel plating has adhered to the steel. In the case of the Harley Benton HQS strings, the nickel plating seems to wear off rather quickly. This in turn leaves the (non-stainless) steel wire bare, which then starts to rust. Each pack of strings lasted about 2-3 weeks of regular playing before they started sounding dull and loosing tension and tune.
Considering that a pack of D'Addario Pro Steels last about 6-8 weeks for me, and that these HQS strings are ~4x as cheap, you could maybe save a tiny amount of money if you leave the HQS strings on for as long as possible. You will have to change strings more often though, which is a PITA.
I will say that these strings are just as good as some other nickel plated strings that cost 2-3x as much, so if you only play non-coated nickel plated strings, these are by far the best choice if you factor in the price.
