I’ve done a few LH EDI-FRA flights in J over the last few years, normally in the A321. I’ve always quite enjoyed them TBH. I like the seat but I guess that’s personal opinion. The first few rows of the A321 have a table fixed in the middle seat - I’m guessing to reduce seat numbers in line with the crewing. My younger son and I have become somewhat accustomed to 2D and F, which have great space.
I like beer in a bottle and German wine, so good scores there! The food has always been hit or miss - I would quite prefer something warm on shorter flights or even a choice, so BA have it there.
I like the Lounges in Frankfurt, the nice premium check in area and priority bag delivery seems to work well.
One thing I have really often found in the last few years though - they often undercut BA intra-Europe J significantly in pricing; even looking ahead to the Faro at new year, they are well over £200 less than BA just now!