Am i right in my understanding that you're basically exchanging BTC for an altcoin with better security features and call this altcoin pBTC. Then, you transact using pBTC instead of BTC and in the end users can exchange the pBTC back for real BTC and withdraw?
https://bitcointalksearch.org/topic/ann-incognito-privacy-for-bitcoin-5183909 That link gives a bit more info. In a way yes, that is how it works if you are using it as some kind of mixer service, but that is not entirely the best way to use incognito. If you hold your funds on incognito, all your assets are private, thus making it completely private. If you use incognito as a mixer service, without enough network movement and a bit of chain analysis your able to _somewhat_ trace a transaction.
Well first, there is price variance when you buy/sell a token, so after the XMR transaction and changing it back to BTC you may end up with different balances than what you wanted. Secondly, there is no additional fee, its free to shield a token, its not free for a coinomi trade (I think, not really into coinomi).
The key point being here, that there are plenty of mixer alternatives that you could use, incognito is not a mixer service, it can be used as one, but it is more of an off- transaction ledger chain where you hold privacy versions of your public crypto assets, are able to transact them off-ledger. completely private within the network, and if there ever were a need for you to need a public version of your token, you could always unshield(burn tokens on incognito network and receive the public version of said token) from pBTC back to BTC.
Hope that clears it up a bit.