I run Connex 808 6/7/8 speed chain on my bike having trawled forums on whether single speed chain is better or not. I’m currently on 8600km with this chain on.
I bought the bike 2nd hand with worn single speed well worn chain and not enough history to compare life spans, but some posts I recall suggested that derailleur chains are as strong, others suggest they could be robuster than single speed chains due to the changing chain line angle on derailleur bikes.
One advantage over single speed chains is price. Most likely due to economies of scale, derailleur chains tent to be slightly cheaper than single speed chains.
I have had better experience with Connex 808 vs Shimano and SRAM chains longevity in over 50,000km of derailleur riding, with up to a third more distance before chain skip issues meant cassette and chain swap. I rarely got more than 4000km on the latter, but the Connex 808 would give me 6000/6500km typically.
When I bought my bike I used a new Connex 808 I had as spare at home once established I didn’t need to purchase single speed chain especially. No issues thus far.
I recently passed 0.75 on chain stretch tool. I’ve adjusted dropouts and still have a bit of room for more stretch. I believe single speed set ups are more forgiving than derailleur on chain stretch performance.
I won’t get into a KMC vs Connex debate, but would suggest a decent quality 8 speed chain should present few performance issues as alternative to single speed chain. They are often cheaper to purchase and based on other posts I have read, may even be more robust and than single speed chains. Even if not, the ground will not open up and swallow you for installing one. It should work fine.
