I think they've made some improvements to the Quest in the last few years. Some of the older reviews mention sketchy quality, but my mower has been trouble-free for almost a year now, and I can say that it was a fabulous investment.
I purchased the bottom-of-the-line Quest (42 inch cut) to replace a 48-inch-cut Husqvarna tractor-type mower. At first I was skeptical that a smaller mower with a slightly smaller engine could replace my Husky. But the salesman said the z-turn would be much more efficient, and that it was better built (I got 7 years out of the Husky before it started spending too much time in the shop).
The salesman was absolutely correct. The smaller eXmark is at least 25 percent faster than the bigger lawn tractor. It can also handle thicker and wetter grass than the old Husky. Those factors alone are worth some extra money. But, the eXmark did cost twice as much as the Husqvarna, so I need to get at least 12 years out of it to feel good about the purchase.
My use is semi-commercial. The mower is used once a week to take care of a large multi-family property. It probably sees no more than 3 hours of use in a week.
Learning to drive a z-turn is a challenge. It's not like the Battlezone game I played as a kid. You *don't* steer with both levers, or you end up stumbling around like a drunken sailor. The technique is to steer with one wheel/lever only. Once you learn that you can do some serious mowing.
Another thing to know is that a z-turn can be extremely dangerous on an incline. And, no, I don't mean tipping, although I've been warned that's a possibility if going straight up a hill. If the slope is not perfectly straight, the mower wanders toward the slope, and there's very little you can do about it. This happens whether traveling up, down, or across any kind of slope. I have many years of experience with small engine riders, and the z-turn took all of my skill not to get myself seriously injured in a few situations. Use care, and don't take the mower into questionable areas.
The Quest gives a great finish cut in all but the tallest of grass. I've had zero maintenance issues during the first year of usage. The only questionable thing about the mower so far is that it can be a little sensitive to starts and restarts - we've learned that a 3/4 choke seems the best setting for a quick startup.