I flew with them for a quick round trip a couple of months ago. Was a last minute ticket and I saved $150+.
Discount Den could be worth it if you fly either multiple times a year or even once with multiple people. Although depending on amount of travel and if you live close enough to an airport, it can be much cheaper to buy in an airport (similar to Spirit).
Don’t rely on Kids Fly Free as the deciding factor, although it’s great if it ends up working for you (specific flights / days of week / advance purchase etc.).
Remember that everything costs extra, so take that into account when comparing pricing. Or figure out how to work within their constraints (buy an under seat carry-on bags if you don’t want to pay $40 to bring a full size one).
If you go into it knowing what to expect, it’s not really all that terrible.
When doing check-in, you can guess which seat you’ll get based off watching the seat map fill up as other people are checking in.
On the outbound, I got an aisle seat with nobody next to me. On the return, I ended up with a middle towards the back, so I waited to board last and then nicely asked the gate agent if there was anything closer to the front with an aisle available. She pulled up the seat map and moved me to an empty row