First of all: This bundle is not needed to play Turbocross! Turbocross is free to play for everyone.
Do you need this bundle? No.
You can unlock all the Pros (characters) with the in-game currency "Combat Credit", which you get by playing the game. This is just a shortcut. The CC Booster is nice, but if you can spend money on this you can also directly buy whatever you want from the in-game store instead. The rest of the items are just cosmetics, no extra stats no nothing.
The only reason I own this is because I got it super cheap in a bundle. If you do not have the chance to get this DLC for a reduced price I would consider buying from the in-game store instead, as it has great deals that in my opinion are better than this set. Half of the Pros included in this set are already avaiable in-game for free (when the game was still actively supported the Pros were rotated, but as of now they're always the same).
Be aware that once you add this to your library the "Combat Credit Boost +500%" will instantly activate and count for your next 5 games. So if you are new or need some more training I'd play around some before activating the DLC, so that you can get the most out of it.
Buying anything from the in-game store or activating this DLC will change your status from "Free Agent" to "Agent", which in turn enables you to trade SMNC items (not Pros) through Steam trade.
Do I recommend this DLC? Honestly, no.
It does what it promises, but so does the in-game store and that in my opinion much better.