For me these swappers are the same centralized p2p exchanges that are presented here https://www.bestchange.com/ but with nice UI.
P2P market is growing, ability to buy/sell GRIN with VISA/MC will be cool.
I have some small experience with similar swappers. There are a lot of them thus services (I know > 70). In fact, they are centralized because the exchange is ultimately carried out through one or another centralized exchange. But these are not exchangers from bestchange[dot]com. Their plus is that the exchange takes place automatically and up to a certain point without any registration. It is very comfortable.
However, this only works up to certain limits. If some control criteria on the exchanges work (they are unspoken, the exchanges do not announce them), for example, the exchange amount exceeds a certain limit, then the coins are frozen, the process goes under manual control and the user is presented with a dilemma - to pass KYC or the coins will actually be confiscated (not returned to the user). In this regard, you should be careful.
These criteria are different for different coins. For example, for XMR, they will require KYC for an amount of about $1,000, but for BTC, about $10,000 is possible (in reality amounts can be very different).
So swappers are very good if the amounts are relatively small and exchanges are not frequent.
Adding another swapper with Grin to the collection