We feed everything sow food. With 35 sows, and most of our weaners sold at 8 weeks, it is better economics for us as we'll only be fattening a few at any one time.
Your pigs will finish quite happily on this - as with all pigs watch their fat levels in the last month and adjust feed accortdingly.
Finisher will let you finish your pigs faster but costs more - so basically it just a matter of economics. Sow food will grow them slower, is cheaper per portion but you need to feed longer. Grower/finisher is faster but more money per portion.
If you're just fattening and after speed then grower/finisher can work out better money. If you're feeding other stuff and after taste and the joy of pigs rather than speed, the sow food can (not will) work out cheaper.