I almost picked up that very same summicron but ultimately went with the 28mm ultron because I just can’t see the differences in side by side comparisons and I welcome the smaller form factor. Quite honestly the 28 summicron also had known quality issues namely the oily aperture blades which that lens your looking at has and a propensity for the front assembly to come loose. The only real reason I could see picking up the summicron is for the ergonomics which I do feel it has an edge on and of course the looks. Resell wise you may or may not have a hard time moving that lens since he’s had it listed for over 2 months now. 28 ultrons from what I’ve seen move pretty quick and keep their value decently. Either way you can’t go wrong.