Part of the issue is that it does a two stage process... so, the first stage takes a couple of seconds when click place an order button... with the nice processing indicator spinner on the page, then indicator goes away, with nothing to indicate - the second stage takes another 5 seconds or more, with with another indicator processing, then finally the order will go through.
Issue is that I'm sure users are going to be impatient and assume that the page is no longer processing and they will refresh or nav away or even click the Place Order again. is this by design? according to PayPal they claim Magento developers develop this extension. it seems like a critical part of the transaction why confuse users with two steps process.