Speed-Power bracelets

I don't know if this has been done already but here goes.

Speed-Power bracelets (SP bracelet for short) are a type of bracelets that allow you to increase your strength and speed to a certain amount.
Here's how it works. Your abilities can be increased by 100% but there's a trick. The increase of speed and power together must not be more than 100% meaning you can have like power 50% speed 50% or power 100% speed 0%. The increase/decrease in speed/power is fairly quick (almost instantaneous)
It can also activate a special mode called 200% mode (probably change the name of the mode) that can increase your power and speed both by 100% but can only be used for a very limited time plus your body is a wreck afterwards. A bit like the blast dial or what was it that really has a heavy burden on the body.

P.S.: Do you think you could make a fruit with such a power or would that be too much or something?

The concept of raising a character's stats by using an item isn't entirely disallowed, per say, but I think there should be just a wee bit more explanation.

You'll have to go into how the character's abilities are increased. This seems to be creeping into the realm of "unexplained magic", and items like that just don't really exist in the One Piece universe, or on the site. If there was some sort of approved Devil Fruit, maybe. I just don't see an inanimate metal object being able to do such a thing.

I think the dial you're trying to refer to is the "reject dial". It absorbs energy then shoots it back out, injuring the user in the process.

The way this is now, I don't think you'd be able to make a Devil's Fruit of the ability approved. You'd have to get more in depth to how it works exactly.

Well okay I can see your point that it's magic-like though I don't really know what to do to make it ''work'' with science or smthing. Making them enchanted bracelets doesn't help, does it?

But what do you mean by get more in depth to how it works?

Either your speed is increased by a certain amount (from your original speed limit) or your strength is increased.
By increasing your speed you can move faster (throwing faster punches, kicks, more likely to avoid stuff, run really fast) but your attacks are in turn less powerful/damaging.
By increasing your power you can attack with a more deadly force (more strength) but become slower and less agile but are also able to withstand a bit more damage yourself. (your muscles being hard and all)

Oh and there has to be a balance. Like I said you have a choice of increasing your strength/speed by 100%. There has to be a balance between strength and speed meaning that the both of them can only add up to a 100% meaning you can have your strength increased by let's say 20% and then your speed can be increased by up to 80%. And so on. You get the point.

Hope this makes it any better (still hoping that maybe it could be a devil fruit)

I think the only possiblity of this fruit would be for it to be a devilfruit.