My 2004. 5 likes the added extra pressure the Edge EZ provides when running either my Smarty or my Hot Juice. It's definitely a boost in power when you flip the EZ to the middle or high pressure level. That said, you can drain the rail down with the Smarty or the Juice on their higher settings probably because I haven't gotten around to the lift pump upgrade yet, I keep waiting for the stock pump to give up and it hasn't.
Also, I recently upgraded my Smarty to the 2006 POD, (Power on demand) with the REVO TNT software which includes many adjustable features including increased rail pressure. I suppose my EZ could be removed now that I have the RP feature within the Smarty programs. I haven't had a chance to try the RP features of the new software and probably wouldn't recommend it unless the EZ was removed because my EZ is the one with the 3 position in cab switch so it's always on with lowest pressure increase being the 20 hp setting. I wouldn't use both the EZ's and the Smarty's rail pressure combined, (one or the other, combined bad things might happen. ) This latest Smarty POD with the REVO TNT is the best I have tried so far but I'm still spoiled by the Edge Juice with Attitude and EZ for their easy push a button or flip a switch adjustability.
Although, back to your original question, yes the stack, (Smarty and EZ) work well, just don't use the two rail pressure increases combined.
Just my 2 cents.