There are no 190's at United either.

UA's Pilots Union would throw a fit if UA brought them in for UAX subcontractors to fly instead of UA mainline pilots. Their scope clause over at UA allows Express carriers to fly jets up to 70 (or maybe 75) seats, so they do have E170s. The 190s can't be flown under UA's banner unless UA mainline ALPA pilots fly them. The 170s, as well as CR7s, do have a small F cabin and a few rows of Economy Plus.

So in terms of room and comfort, UA's express outsourcers have a significantly better option than CO's barbie-jets. Though considering many are flown by Mesa and others by Republic subsidiary Shuttle America with wacky screaming FA seatpocket rules, UAX ain't so hot. Though a lot more comfortable in E+ or F on a few-hundred mile E170 or CR7 than on the CO ExpressJet 1043 mile RDU-IAH on a 145, even though the service is better.

There are quite a few posts in the "ask the pilot" thread on the UA board about this.