A folding elliptical is a last resort in my opinion. Try not to stray from a ridged frame construction.
Basically the T 7.90 is the folding version (Space Saver) of the RL 6.0. To the surprise of many, this folding design has been very reliable and always seems to work. The machine folds and unfolds straight and never seems to be in a bind when the arms are reattached. Again if this is a choice and space is not a factor always go with the solid construction.