I haven't used 2checkout myself since 2005 when I dumped it because it was so unreliable, and the module at that time was also flakey. Never looked back, and I generally avoid every mention of them.

Maybe I'm too biased about it still, but if the module is still having problems in recent years, then that suggests that the 2checkout gateway is still architected poorly and the module is being forced to go through needless hoops in order to confirm a payment. If the gateway is still unreliable, then that's telling.