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Do they feel more like bridge cables (Roto), or wet spaghetti (TI)?
I know what you mean but I would like to point out that Roto flats are only bridge cables if you buy gauges that feel like bridge cables. You may have to go slightly lighter than the gauges you normally use for a similar feel though.
Also, the stiffness of Roto flats will allow you to set the action lower than with most other strings. I normally use 45-105 with most other strings. If I change to Roto 45-105 without doing a setup I find them unplayable and my hands start hurting after 5 minutes. After doing a proper setup and lowering the action they feel great and I can play them all night.
(I love TI flats btw but I wish they would re-design them with just a tiny bit more tension on the A-string...).