I cant say I've had any experience with this model machine but I once owned an RF30 mill drill which was pretty flimsy and tended to vibrate and flex a lot. Most of the vibration was caused by the motor which was a cheap chinese thing, I suspect if i could have got a smoother running motor fitted the surface finish on the milling jobs would have no doubt been better. If your machine has handles on the leadscrews (or if you can somehow adapt handles to it to try milling) I would do some manual milling and see how it runs, this will give you an indication of how it could run when retrofitted. I suspect it also depends on what you intend milling as to how good it will be (may be ok for al but maybe not steel).
Hope it works out ok.