I can compare it to my 04 Civic DX as that'll closely relate to your EX.
The Mirage definitely has less power. Though, I wouldn't say at all that it is under powered. Its really completely fine for daily driving and I almost never have to rev it way up to stay with traffic. It does handle lower rpm better than the Civic which is nice.
The Mirage out of the box doesn't handle nearly as well as the Civic. The Civic feels solid and well planted. The Mirage is rolly polly and has a pretty soft suspension. They tightened things up in subsequent years (2015 and again in 2017), 2014 is the softest. But, I actually think the Civic feels better than most cars I've driven handling wise. I really enjoyed how the Civic rode. The sway bar I made for the Mirage definitely helps a lot, but its still not as nice as the Civic.
The interior is pretty comparable IMO. I know the Civic has a bit more 'soft touch' stuff in it, but I honestly can't tell much at all. I don't mind the hard plastic as its really nice and durable, and easy to clean. Its pretty subjective, but I like the look of the Mirage interior a bit more than the Civic. Comfort wise, they're pretty comparable. I am a fairly short guy at around 5'6".
MPG wise I haven't been able to really tell too much. In the 6 months I drove the Civic (which was nearly all summer driving), I averaged 43 mpg. I had a high of 47 mpg and a low of 38 mpg. In the 3ish months I've driven the Mirage (all the harshest months of winter) I've averaged 42 mpg. I've had a high of 44 mpg and a low of 38 mpg. I fully expect to be over 50 mpg with the Mirage in summer. This is with pretty mild ecodriving. I haven't been turning the engine off or anything like that, just driving conservatively, timing lights, and avoiding brake use.
Reliability has been pretty great with the Mirages. Problems are very few on
MirageForum. So, I'm not concerned with possible future issues.
If you have any interest in the car, I'd suggest going and driving one. If you end up liking it, setup email alerts on craigslist, autotrader and cars.com for when new listing appear. Wait for a great deal on a used one like I did and you almost can't go wrong.
I do find it pretty hilarious that I was able to get my 2014 Mirage for just a few hundred dollars considering the Civic is worth nearly $3500 on craigslist.