I'm not familiar with that specific lens, but two things occur to me.
(1) Expensive camera plus cheap lens = bad results. Cheap camera plus expensive lens = good results. It seems a bit odd to have a great camera like that and stick a £99 lens on the front.
(2) For portraits you generally want fast apertures. That lens is only f/4 at the long end. You'd do better looking for an f/2.8 or f/2 lens.
Has to be the 50mm F1.4 or the 85mm F1.8 depending on distance available on a budget surely? Then 135mm F2 and ultimately 70-200mm F2.8.
None will be £99 though.