I think the best description is it is “variable”, Paul. Aware of the reputation, I checked my 259B when it arrived and I can’t find fault with it. It’s been working for 10years without issue.
The other issue is optimistic power handling specs. MFJ are not alone here, a lot of 3kW ATUs only have that power rating when the antenna is better than 1:1.5 in the 1st place 