Never seen one combined with a stepdown before.
The more joules the better.
The most important feature is up to you to decide on.
For ppl that want to fully protect their equipment period. You want a Surge that auto cuts power off to its outlets once its past its joules rating.
Most Surges, once they are beyond their limit have a protection LED. If its not lit, its not protecting anymore and is just acting like a regular powerstrip.
How often do you check a Surge Protector's lights to see if they are still on? Most never do.
Good quality surges are usually $30 or more.
Here is a good example of one on Amazon atm for $24:
http://a.co/d/5BXw7ai
- 2395 joules
- Auto cut-off version
Other things to consider is specific needs. # of outlets, wall plugin style, etc.