Thanks for your post.
SQL Prompt 5 should be able to co-exist with the native intellisense. There are a few features (like parenthesis matching) that the native tool supports that we don't, so they can both be enabled.
However, the candidate list pop-up should only be enabled for one of them, or they will interfere with each other.
It sounds like for some reason Tools > Options > Text Editor > Transact SQL > General > Auto list members is still enabled, which would cause the native list to pop-up as well.
The main advantage over the native intelisense is the additional formatting and non-code completion features: http://www.red-gate.com/products/sql-de ... ure-matrix
There is also advantages in the way SQL Prompt makes suggestions for code completion, but I have to say I'm not entirely sure how sophisticated the native intelisense has become to confirm if we still have an advantage in that area.
I hope this helps.