Sorry for the long post but I want to share the info I found. I think the Briggs Pro engine is probably ok for non-commercial use but personally I would not risk it if you can get a Kawasaki for similar money. If you like the Simplicity better and are happy with a good but not commercial grade motor and you can save at least $700 versus the price of the mower with a Kawasaki then the Simplicity with the Briggs Pro may be a good choice.
The Briggs Pros I have seen have the electronic fuel management system which is supposed to be more like a car. It's electronically controlled and I think it has no choke, it does that for you so you just turn the key and it does the rest. Sounds nice but I don't know how proven it is as I think it's fairly new and that makes me nervous. You might want to research that further. I can tell you that in my personal opinion the Simplicity tractors I looked at are built far better than the comparable John Deeres. Don't get me wrong, I think very highly of the JDs and was actually set on buying one but the Simplicities really impressed me, which is why I bought one instead of the JD. I'm not sure how the ZTRs stack up to each other but I have used one of the very expensive high end commercial JD ZTRs and it was an impressive machine but cost well over $10,000.
Personally I will not buy a non-commercial motor again after having nothing but trouble with two Kohler Commands. The only Briggs motor I would consider commercial is the v-twin Vanguard since it is made by Daihatsu, an excellent Japanese manufacturer which is owned 51% by Toyota and produces parts and some entire cars for Toyota, mostly in non-US markets. That's a big difference from the rest of the Briggs line. (single cyclinder Vanguards are still made in the US by Briggs I think). All other Briggs motors are made by Briggs in the US and I hate to say this but they are not in the same class as the Japanese made Vanguards. I honestly don't know if Kawasaki makes different grade motors like everyone else, they probably do. I admit I tend to say all Kawasakis are great but you should try and find out exactly what model Kawasaki motor is on the JD and is it actually a commercial grade motor or not.
One thing I like about the 23hp Vanguard on my Simplicity is the oil cooler. One of my Kohler Commands ran hot all the time, no matter what I or the dealer did to try and help it run cooler, maybe an oil cooler would have helped. Might not be a big deal but I am glad my new mower has it, perhaps the Kawasakis have them too.
My best advice is not to be in a hurry if you can help it (but the grass is growing fast I know). I did a lot of research which is why I was comfortable going with a Simplcity with a Briggs Vanguard when I had been set on a JD with a Kawasaki. Most people lump motors together by brand but you really can't do that. You need to know what you are buying and you need to do all you can to try to eliminate the chances of down the road saying, "Doh, I knew I should have bought the other one!"