Yes, my wife and I have used them out of Lansing, MI.

Their planes are new and clean, the service is better than many domestic airlines, and in our experience they have kept to the schedule.  We used them to both Las Vegas and Florida (both non-charter flights).

On Saturday, I put a couple of friends of mine on the flight to Tampa because of a family emergency.

By the way, as with Southwest you can buy one-way tickets without paying any penalty.  Here's a link to their website. 

http://www.allegiantair.com/?gcl

Bob U.