I think Schwalbe fixed the problems with the splitting sidewalls. Ive had Schwalbe marathon plus tyres for months and ive been across some pretty rough parts of tow path and its just perfect. Did your tyres have the reflective ring on the sidewall?
I think they did. Have thrown them away, so can't check. They were the 25mm and were fine for the first winter, maybe the second, Then when I put them on for the last time, they developed a "bump" with each rotation and I found that the side wall was splitting away from the main tread. I put it down to the puncture protection layer, probably being the same as used for the wider tyres, so put a greater strain on the 25mm widths. The city contacts have been fine, but might try the M+ again when the contacts are worn.
Cheers Keith