Frame sliders are always a bit of a gamble in my opinion. I've been racing for about 12 years now, and crashed so many times that I've lost count really... Got to be somewhere between 20-30 times now...
I've crashed numerous bikes both with frame sliders, and without frame sliders. And in some crashes, the frame sliders have helped a bit with damage control, and in other crashes they have even made it worse. Sometimes they get torn off/out, damaging engine mounts and mounting points. Sometimes they have been bent/flipped around, causing more damage in the area around the slider. If the bike starts tumbling, they are no good either. And in most of the crashes that the sliders have actually helped a bit with damage control, we've had to replace/repair/repaint the fairings anyway, but maybe with a bit less work.
Anyway, I think it's a bit of a gamble. Sometimes they help, sometimes they make it worse, and in most crashes they don't make any difference at all. I'd put my money on a good protection for the engine casing instead. We are using R&G at the moment, and are pleased with them, but there are a lot of different brands and solutions out there that work really well. They are actually mandatory in our regulations now, since last year I believe...
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