I have 2 of each olfa size 28,45 & 60mm, and only 1 of the 18mm.
The 18mm is my LEAST used although when I am working on small
projects I will use it on a small 4x6 cutting mat near the machine and
it works perfectly for me, but most often I just either the 45 or 60mm.
Several years ago I got lucky and won a bid on ebay that consisted of
1 of each size cutter, plus a chenille cutter, replacements blades in the
sizes 18mm=20, 28=10, 45=10, 60=5 & chenille blade=1. ALL of this
for the winning bid of $52.50 plus $5.75 for shipping.
Never have seen another whopper of a deal like that since.