You're limited with modifiers as the EX/EXD range have their own fitment, unique to them,

Where?
I've got to say that the thing that would put me off is the power, 150 aint much.
If it was my first and only gun, Id be looking at 400 watt secs.
150 Ws isn't much, but power is the least important consideration - personally I would be more concerned about build quality, colour temperature and flash energy consistency and the availability of accessories before I worried too much about power.
For amateur use, where large prints are unlikely to be important, you can effectively double the power simply by changing the camera ISO from 100 to 200 without worrying too much about loss of image quality.