Summitars are softish at 2 and 2.8 as we most lenses of the era. The performance is superb at 5.6 and 8.
3.5 red scale elmars are also nice stopped down. Mine performs better than my two Summitars at 3.5 and 4. It is the most collapsible Leica lens.
Summitars have odd filter threads so you need an expensive adapter or dedicated Summitar filters. The lens shade is a big barn door one or you have to cobble something. Try heavystar on ebay.
All tend to be foggy and have soft coatings.