go to the code-reader-getting place and pick the one that costs $80 to $100. it'll do all you need. i don't "think" there's much feature differential between the brands at that price point.
do your self a favor and bring the lotus to the store and try to get your new toy to talk to the car's computer before you leave the parking lot. it'll save you a trip it there's an incompatibility (chances are low this'll be the case).
My 2005 Lotus used the ISO9141 interface. Later models may use CAN - this was mandatory by 2008 but it would not surprise me if Lotus got a waiver and still uses ISO9141.
Bottom end is a laptop based interface for $20-$50. Do a search on ebay for Elm327.
Middle is a handheld system which can read and clear codes. Usually $60 - $100. Again, searching for 'obdii reader' on ebay will give you an idea of features and price.
I also have a scanguage, which is aimed at displaying information to aid driving style to help fuel economy. eg instant mpg, trip mpg, fuel used, range etc. They specifically list the Lotus as being one of the cars which the scanguage does not work on, but it seems odd becasue any other scan tool worked with my Elise when I still had the Toyota engine.