After working with Rotozip tools on a jobsite I learned what they did well, which was cut sheetrock and suspended ceiling panels, and what they did not cut very well, which was plywood paneling and wood. They cut it, but it was a very rough cut. All of it was done freehand, and when cutting there was considerable side pull similar to what happens when you try to increase a hole size with an electric drill and a twist bit. After gaining experience with Rotozip I never bought one for my shop. They have uses, but not enough to justify the cost, at least for me.
A few years back my daughter-in-law wanted help cutting out large drawings of cartoon characters from 1/4 luan plywood. I tried using a sabre saw (hand held jig saw) and decided that it just wasn't right for the job, so I installed an adapter and a Rotozip bit in an old Makita plunge router. Laying the plywood on some sheet foam insulation I was able to cut out these characters with a minimum of chipout and when cutting it slow I discovered that the side pull was very manageable. The project turned out very well, and I discovered a way to use Rotozip bits successfully. The foam backing does a great job of keeping the bit from hitting anything solid, holds the sawdust, and most importantly, it keeps the edges of the cut from having the significant chipout that had turned me off to the Rotozip system so many years ago. I still don't own a Rotozip, but do keep the 1/4-1/8 adapter and some Rotozip bits in my shop now. They still aren't for precision cuts, but they have their place in woodworking.