We purchased one of these at Christmas for our little boys (one who turns 4 in September) and we really like it. The one we have is by Little Tykes and has a 250 pound maximum, so an adult can go in with him if he wants. To lessen the risk of tears we have a "no shoes" policy. Also, we put it on a tarp on the grass. We use the tarp so that any random sticks or rocks on the grass that we don't see hopefully won't poke it. Also, we don't put it on concrete. One word of advice: on the one we have (which I assume is similar to the one you're looking at--same manufacturer) there is a mesh opening in the back which has velcro to close the opening. Make sure the velcro is secure to close the mesh opening. Our son was jumping wildly and almost fell out because we didn't velcro the back.
Since we haven't had any problems with it, we haven't experienced problems with the warranty. But, if you get a few uses out of it the investment is certainly cheaper than renting one each time. So, you aren't really out that much money in the long run.
Have fun (I even like it !)!