Beware the copies!!!!

I’d put the money towards a proper mill. More rigid, bigger clamping area, bigger travel, easier to set up, etc

I’m not sure how useful the longer 4 slot one will be as you run a greater risk of the bottom of the table hitting the bed so travel may not be any more than the 3 slot

Another vote for putting the money into a real milling machine.

Milling slides on lathes are very limited in comparison with a real mill; nowhere near as rigid and they only provide a tiny work space.   Good work is possible, but slides take ages to set-up, and are then only able to take light cuts over short distances. Frustrating.  On a very good day I scored mine no better than ³⁄₁₀.

Slides were popular back when it was almost impossible for amateurs to own a real mill.  Today, we can, and should!  In many workshops I suspect a mill is more useful than a lathe.  Certainly wonderful to own both.

Not having enough room for a milling machine is the only good reason I can think of for owning a lathe slide.

Dave