First off, afaik, its usb to serial. The *TTL* designation means transistor-to-transistor-logic, which is different altogether and refers more to hardware gates and related.
Also most of reprap electronics use FT232RL and works ok, i also have one and also works ok on a vanilla mendel. I think the change away from FT232 occurred only with use of arduino mega which started to use an programmed atmel chip instead of ft232, but except that, probably the most used reprap usb to serial converter is still ft232.
If you have any doubts, buy a module UM232R, thats a complete solution for usb-serial conversion with ft232rl and all support components.
Also most of reprap electronics use FT232RL and works ok, i also have one and also works ok on a vanilla mendel. I think the change away from FT232 occurred only with use of arduino mega which started to use an programmed atmel chip instead of ft232, but except that, probably the most used reprap usb to serial converter is still ft232.
If you have any doubts, buy a module UM232R, thats a complete solution for usb-serial conversion with ft232rl and all support components.