Hi John
Loch Ba is a stunningly beautiful loch and will be the first port of call once the wife allows me to buy my float-tube. I fished it on a sunny April day a few years ago. Was only once up there that it reminded us how high the moor actually is (1,000ft and very very exposed). Basically we were only a couple of hundred yards below the snow line and there was absolutely nothing doing. Also it is very shallow and weedy (even then)...had to hunt around for deeper channels.
It is a huge network and would be best to yomp to the more remote bays as the road side part of covered in balls of discarded nylon and bbq trays - just think, if you could catch them at it they would never find the bodies up there
Worth adding it is illegal and rather unsporting to use two rods for trout - unless your mate is intending to fish with one in each hand simultaneously

If you are going up there why not take an extra flyrod and teach your mate if the fishing turns out to be sluggish.
Also worth noting that if he is long casting bubble floats using a spinning rod he is likely to deep hook fish...particularly small wild brownies.
In summary - if you are after lots of fish would be worth waiting till you don't need to wear your thermals...tight lines