Most oven sprays are caustic. Caustic soda or the like. They do work but they're hella unpleasant to use. Wear thick rubber gloves, tie a rag over your face so you're not directly breathing the fumes (I only do this while spraying it) and use steel wool or the like to scrub. For trays, spray them w/caustic and then leave them for a couple of hours. Clean them once and if they're still dirty leave them to soak in the sink in very hot water and dishwashing detergent. Whatever the case, WASH THEM after using caustic as it's nasty stuff.

Bicarb and vinegar does work but it takes much more physical effort and isn't as effective at getting the really baked on grunge.

I used to be a kitchen hand and we cleaned our ovens once a week. Hope this helps.