BMS tunes are very safe and unbelievably reliable in the N54's.
I run a JB4 and not a single issue. If money permits I strongly recommend the JB4 over their smaller mod you are looking at. I understand $ can be an issue tho. Look on the forums, you can probably get a JB4 cheaper than what it is brand new!
2008 335i - JB4 / BMS DCI / Premium Package / Sport Package / 6AT