I bought a 154S with the EFI Kohler back in March. It was a demo unit and had 4 hours on it. I paid $6300 out the door after tax.
I use it to mow my own yard (a few acres) and nothing else and I've put only about 20 hours on it. It is a very well built machine, but I'd probably step up to the 700 or 900 if mowing commercially. When you see those machines next to the 100s, they're just on another level. No complaints with mine with how I use it, though!
The machine cuts very well and cuts fast. It replaced a garden tractor with the same specs 27hp/54". The Cub mows my yard in half the time.
I put Gator blades on it, as I've had great success with them in the past. The stock blades seemed to be fine.
I bought the S model due to the hills I have here in Virginia. It handles the hills just fine, though I feel that the front end gets a little light at times going uphill.
The only complaint I have is that deck height pin pops out at times.
New vs. Old