I have a single bar cutter from Custom Craft Tools, and it is awesome. I had a Bud cutter that was made of wood (I think that has changed) that I liked, but found limiting if I was wanting to cut a loaf horizontally - for example, cutting a 9" loaf into three pieces 3" long as in a Taiwan swirl, etc. The screw and plate for the stopper can easily be completely romoved from the CCT cutter, which is a big plus over what my Bud cutter could do.
I bought my single cutter from CCT before they introduced the caterpillar/hercules. I did buy a caterpillar and love that too, but when I'm just cutting a loaf I always reach for my single cutter first. If I could only keep one (or didn't have one and was looking to buy) I think I would have to choose the caterpillar as the ability to split slabs is a huge bonus.
The only problem for me with a multi bar cutter is that there really isn't any flexibility in the size of the bars. This is only occasionally an issue, but still something to consider. I don't sell and enjoy cutting soap, so I'm not dealing with large quantities of soap that needs to be cut. In that case, I can see the appeal of a multibar cutter.
I think I remember Katie at Royalty Soaps trying out and endorsing a relatively inexpensive single bar cutter she found on Amazon. You could check her YouTube videos - I saw one recently where she was using it (I think when she was using a Bramble Berry kit).