I have over 700 hours of Tomahawk time, including countless stalls and lots of spins.
When Piper decided to build a trainer to compete with Cessna, they asked a lot of experienced flight instructors and examiners what they would like in a trainer. For the most part, they said they would like a roomier cockpit, good visibility, cost efficiency, and flight characteristics that would make a student fly it properly and not hide mistakes. They built the Tomahawk to have all those qualities.
Most of the complaints about Tomahawks are based on stall/spin situations. If you learned to fly in a 150 or 152 you know you can recover from a spin by simply closing your eyes, letting go of the controls and crossing your arms and legs. If you are stalling a 150 you can also raise a wing with the ailerons during a stall without worrying too much about ending up in a spin.
The Tomahawk requires the proper technique for both stalls and spins. If you are in a stall you must keep the wings level with the rudder, just like all your flight manuals say you do. When a wing drops during a stall in a Tomahawk and a student tries to use the yoke, it stalls that side even more and the airplane goes into an incipient spin until you correct with the rudder. I see it everyday. Then I get into our school's 172 and I watch Commercial students correct that same situation with improper technique, using the yoke. They can get away with it and when I correct them I suspect they don't really take it to heart because they have not seen the consequences.
I have spun the Tomahawk on many occasions for both student pilots and CFI candidates. The most I've done is a 5 turn spin. If you just let go of the the yoke, it stays in the spin. Why shouldn't it? You must use the standard spin recovery technique just like all your flight manuals say. With proper technique, I have never had a problem recovering from a spin.
I think the Tomahawk is a fantastic trainer and I think it produces a better pilot than a 150/152. I am not completely biased, because I went through most of my Private training in a 150, then had to move and came to a school that uses Tomahawks. I remeber finding out that it was harder to fly and for the first time I really did need those foot pedals on the floor.
What good does it do to teach a student how to recover from a spin, only to let them find out they can just let go of the controls? That same student will later get into a Tomahawk and claim that it won't recover from a spin. Or they will claim they did a gentle stall and it went right into a spin. That's a load of crap. I have all my pre-solo students stall the Tomahawk at 6000' with full back pressure and just hold it in the stall all the way down to 3000', never moving the yoke from its neutral, full aft position. Lightly dancing on the rudders to keep the wings level, the thing never gets near a spin. If they can do it properly anybody can.
Also, according to our A&P, the wings are not an AD. It is a life-limited part. It was designed to be replaced at 11,000 hours from day one. An AD is for a problem that arises after the plane rolls out of the factory. The Tomahawk also has a life-limited elevator trim spring. I don't remember how long it lasts, but you can find the numbers for both on the Type Certificate Data Sheet. The ADs won't mention either.
As for performance on grass strips, I think it would be okay. Obviously a taildragger would be better, but the Tomahawk would do just as well as any tricycle gear plane. Like the previous poser said, the Tomamhawk came with two different size wheels depending on the year. Make sure you get the big wheels.