Hello,
The difference often lies in how the exchange is carried out behind the scenes.
With ChangeNOW, or another traditional swap service, you send your LTC to a deposit address. The platform actually receives the funds, then sends the POLs from its own wallets to your address. On the blockchain, you can therefore see two distinct operations: the deposit of the LTC, then the sending of the POLs. The deposit is thus easily traceable.
With Leodex and some internal exchange services, the funds may already be held in a centralized system. When converting LTC to POL, the platform can simply update the balances in its database, without executing a transaction on the blockchain. This is comparable to a transfer between two customers of the same bank: the balances change, but no external transfer takes place.
In this case, no POL deposit appears on the blockchain, and analytical tools cannot detect the conversion. Only the platform knows that an exchange has occurred. However, if you then withdraw your POLs to an external wallet, a transaction is created and becomes publicly visible.
In summary, with ChangeNOW, the exchange generally involves transactions visible on the blockchain. With an internal transfer on Leodex, it might be a simple balance change, invisible on the blockchain until an external withdrawal. This is also what can make these conversions faster, since they avoid intermediate confirmation delays.