I dont understand the bonus Prestige

Yes, this might help (Taken from the DBD Reddit):

When being close to the 170 perk tiers, it's better to invest some more BP to get to the 170 perk tiers.

I would say if you just leveled to P0 L50 without doing additional webs (so you only have around 55-60 perk tiers), then sure prestige before the update. But the more perk tiers you have bought, the more items, addons and offerings you will have bought as well, which you will all lose when prestiging before the update.

So maybe something llike this:

When P0 L50 with less than 120 perk tiers, just prestige.

When P0 L50 with more than 120 perk tiers but less than 170, try to invest BP to get to 170 perk tiers.

When P0 L50 with 170 perk tiers or more, don't prestige and wait for midchapter.

This is actually a decision I have to make for my Yuichi and Haddie, bc they are both P0 L50 with 130 per tiers. I'm not sure if I can manage to get them to 170 perk tiers in time (should be able to boost them greatly with the rank reset BP though). But I also have 20+ event flans on them, so I surely will not prestige them before midchapter hits. Guess I have to prestige them in the new system then to get their perks for all survivors.

Perks come in 3 tiers, each one of those counts as a perk tier.

So say you have 10 purple tier 3 perks, and 5 yellow tier 1 perks, that would total 35 perk tiers.

For easy reference, each page has 15 perks, and if that's an entire page of purple, that counts for 45 perk tiers.