One of the benefits of using a SS specific hub is that the spokes are further outboard, making for a stronger wheel. Other than that, they’re generally a bit lighter, and also tend to have threaded axles so you can use allen bolts instead of QR, which is handy if you have a disc brake. You can cut threads into the axle of your cassette hub, or fit a solid axle and nuts, of course.
White Industries freehubs are very lovely, and last a long time. The other benefit is that servicing or greasing the guts is very, very easy – undo the pin spanner and it’s there. Cassette hub is: remove sprockets, remove axle and bearings, find 10mm allen key, fat mate and workbench with vice, etc etc.
If you’ve got a standard rear wheel it’s worth using that first – you can also run different sized cogs to give more than one speed (handy if you ride out to rides on the road) or to fine tune your ratio. If you’re happy with the ratios, can tune the chainline (external bearing BBs are good, as you can use spacers), and want a fit and forget hub, then something like an On-One + White Industries will be pretty good.
My advice? Starting from scratch, cost out the two options. Building a dishless rear wheel is as easy as it gets, so you may find that the total DIY cost is cheaper than a cassette rear wheel, especially if you have a rim hanging around.