I owned an RD11 which as you point out is the daddy of the RD11s. I believe that the main difference was the shape of the armboard - round and small for the latter , long like an Lp12 for the former. The shape of the subchasis is also different but not masively.
I also now own several DD's - SP10, Sony 2250, JVC QL70, Denon DP60L and a couple of other Technics decks.
What you should notice with the Ariston when set up properly is that it is a very engaging, lively 'fun' sound. It plays funk, soul, dance music etc excellently. Really used to get me wanting to shake my butt (which ain't pretty). I never found it to be a subtle sound but I also never got fatigued by it.
The down side is that after a DD you will probably notice the lesser pitch stabilty and wow & flutter. You will most likely hear this on high notes, extended notes, piano, strings etc. it's a subtlely audible difference but IMHO & IME it by no means means the Ariston is not worth keeping.
Also Aristons are a PITA to set up for some reason but once done they tend to stay set up longer than an LP12 and there is a real sweet spot sound wise once the suspension is bouncing nicely. You'll know when you've got it as the sound suddenly focuses in a very noticeable way.They are however a lovely TT and one of the better vintage BD's IMO. Ariston made a few fine decks that are worth trying out.
If you like it then try a few little tweaks that improve it - Plywood baseboard, dynamat or cork damping the underside of the top plate, cork damping on the subchasis, Dynamat damping of the platter - only needs to be on the outer inside rim of the platter - and a better platter mat.
Placing them on a wall shelf or isolation platform makes a difference too.
Good luck and let us know your thoughts as IME they are worth keeping as a 2nd TT if not as your main.