Wow that TW90 looks like an awesome grinder. Not a bad price either. Wonder how smooth it runs though. About building my own, while I like to think my knives are good quality, im not skilled or knowledgable enough to build my own. It would probably resemble Homer Simpsons "artwork".
If you only have 1 grinder, I think the versatility the tool-bar system offers is important.
Time spent on changeover can be irritating and interrupt your workflow.
I think that is much more important to me than the difference in smoothness from one to another.
I often see the Burr King recommended as the smoothest
I'm not sure why "smoothness" is such an issue.
In the admittedly few types of grinders I've tried, vibration wasn't an issue.
The TW build quality looks great, I don't imagine he is putting out an unbalanced product.
The only issue i can think that "smoothness" applies to is a KMG/nwg style with belt and pulley drive as compared to direct drive.
I believe that a fully keyed slot drive shaft and the inherent imbalance in belts leads to the perceived "unsmoothness"
I prefer precision ground steel, but
The TW90 SG attachment is interesting and would allow you to use cheaper mill stock and PG the flats and tapers in yourself.
If I was buying my first and only grinder, & had the budget to buy it, TW90 would be in the top of the picks.
Or
a Bader 3, separate Horizontal grinder, plus the SG attachment for the tw90