I'm not sure the armrest will make much difference...if they are large build the fixed armrest will probably help contain them rather than spilling into their neighbours space. For me the bigger issue is the shoulder space. If they are of largish build they are likely to find they are wider than the seat.
I'm a 5ft10 woman and my shoulders are wider than these seats. It's a bit of a nightmare as there's really little to do about it save twist in the seat, or encroach on my neighbour - unless they happen to be a pretty normal build themselves in which case they'd be trying to encroach on me!