I have both, and both are great plants, but I like East Friesland a little more. It is nice and tidy, growing in a 'controlled' clump. May Night tends to sprawl with the branching kind of helter skelter. MN does bloom a little darker and longer, but is harder to cut back for a little rebloom. With the way the stems sprawl I sometimes have a hard time deciding where to cut back to. Both May Night and East Friesland have given me babies, but the offspring aren't the same as the parent plants. As coolplantsguy said...I don't recommend collecting seed with the thoughts of growing more of the same.

Deadheading your May Night (Mainacht)is not necessary unless you want to remove the old spent blooms for asthic reasons.Right below the first bloom you should see secondary growth that is where your new blooms are developing. Remove just the bloom just above that secondary growth. Does that make sense?

When I lived in western Massachusetts (USDA Zone 5), I cut back my S. nemerosa `East Friesland' to the ground after the stems died back. I did not mulch. If you do mulch, you should put it down after the tops are gone. I'd use hardwood bark mulch (no wood fibers) and pull them back when ground frost stsrts to disappear. Where you are, mulching is important in controlling the depth of frost penetration and to prevent frost heaving of autumn-planted ornamentals.

I moved a Salvia May Night last summer and just unceremoniously plunked it into a hole I dug in ordinary dirt close to and under a Pin Oak by our driveway where it only gets sun from about 2 till 5 or less. Its in very dry unimproved soil so maybe its moisture or too rich soil causing the flop? Mine actually looks good and bloomed same as usual. I transplanted another part of it in even more shade down by a shrub where you can't really see it just because I didn't have the heart to toss it, both bloomed this spring and didn't flop, frankly this plant got boring to me so I relegated it to unimportant spots and thats why its where it is now, poor thing. I'm editing to add that it gets more sun in spring before the neighbors blasted Pin Oak monster leafs out, the rest of the season it just sits there but it did bloom twice because I deadheaded it. My experience was catmint got too bushy & tall in morning sun only making it messy looking compared to the nice silver & xeric looking compact & tight form they have in full sun, that mattered to me a lot more than the blooms. It bloomed just fine in spring but I got rid of it because I didn't like the looks of it and didn't try to transplant it. I always felt compelled to trim it back and I hate the smell of it. I learned that if you dig out the salvia it will come back because the roots are so deep and extensive. It might take a about three digging sessions to get it all out if its been growing there for a while.