On paper this asset solves all of my text problems, so I'd really like to make it work - but it starts chugging with as few as 100 characters; essentially meaning I'd need a new object for every sentence or two. I don't really consider that to be usable.
I don't mean to criticize your code (I haven't even looked at it yet), but I feel like something is being done very wrong for it to perform this badly and you either need to find out what that something is, or separate out some of the more expensive functionality - enabling it only if it's used. I understand that Unity's own editor code is often very poorly optimized, but there are definitely ways to work around that.
Now, as for a prefab: if it's something that allows me to set a single text area (rect where text appears) and then automatically creates STM objects as needed, I would consider that to be a satisfactory workaround. I don't want to have to micro-manage a bunch of separate text areas though.
If you could do that relatively soon (next few weeks), it would work for me - ideally also committing to fix the underlying performance issues at some point. If not, I don't think the asset will work for me and I'd need a refund, as I don't think it currently meets the lightweight performance claims.