Hiya,
I have tried both. I found quads heavier and nearly had heart attack when tried crossovers on them!But after watching people and youtube vids of people on quads doing artistic skating, it is very possible to transfer Ice moves to them. I think if you go for quads you need to adapt your technique from Ice. Also from the searches I did, I found the quads to be much more expensive, even second hand (unless you buy a leisure pair which are very heavy) That being said you have to adjust a little on the inlines as you cannot be sliding your foot you have to lift. My personal opinion is, if you want the off Ice to support the on ice, go for the inlines.
My daughter has Inlines, she has an Edea Ice boot with an elite blade (will post link later when not on phone) She does most things on them that she does on ice. The blades are quite easy to measure and fit yourself.
I have a beginner boot and blade (but I don't use very often and am equally rubbish at ice skating so dont take my opinions as gospel!) But I would recommend if you are past Skate Uk that you get a better boot than beginner for support.
The off ice inlines have wheels that simulate edges but have only seen one pair standard inlines, which didn't and are more rounded.
Hope that helps a little, I have a good ability for confusing people with my indecisiveness
Will post links later x
http://off-iceskates.com/shophttps://www.youtube.com/watch?v=tWnESlMmkG8 (Random one off youtube)
Quads ...
https://www.youtube.com/watch?v=ykapZ-KIxl0&t=175s (Amazing
)