Yes it is better than an underhood filter. no better or worse than the stock airbox other than a conical air filter has more surface area.
By the way, if your current air filter is under the hood then it's not a CAI. It's an HAI. lol
Pulling air from outside if the engine bay is always desireable over pulling it from within.
The ram air effect of the march kit is negligable. Shortly after I installed mine, I was able to document an average of 8 additional miles from 13 gallons of gas over the Pensylvania Turnepike (no stop lights). In town, there was no measurable advantage.