Hi,
It's not the same API, so PayPal doesn't offer the same capabilities.
So because the option is not there doesn't mean that we didn't want to add it (or didn't have the time) but more likely that this option is just not possible with the new API.
For example, there is no "send details of the order" option because the new API always require all the details of the order. So it's as if that option would be always activated in that new plugin.
Also, the new API brings some nice new things. For one thing, the customer stays on your website while still maintaining PCI DSS compliance. If you choose the credit card option there, it directly opens the credit card form, without any hassle like with the old API.
Also, with the next version of HikaShop, we'll add a new "funding" option which will allow you to accept other payment methods like "pay later", "sofort", "ideal", etc via the PayPal checkout plugin, offering more payment methods to your customers. And that is not possible with the old API.
All in all, I personally feel the new API is much better for the user and thus for the merchant too, without even going in the fact that the old API will probably be discountinued at some point in the future.