I did my CMEL and MEI in the Twinkie, even some time in Patrick's plane (his is sweet by the way). Now I instruct in the Seminole.
If you have all Seminole time, the Twinkie is going to be a bit of a chore at first.
The main difference is the critical engine. The Twinkie actually requires a good deal of rudder when single engine critical. The 'Nole single engine is almost effortless in comparision IMO.
As mentioned before, the Twinkie is a challenge to land well and consistently. I greased every landing during my CMEL, but for some reason it was hit or miss during MEI training. It really does land like a Mooney; Sitting low to the ground, it is VERY sensitive in ground effect and can easily balloon or wheelbarrow on with just a little too much elevator either way.
Finally, Vmc exists a ways above the stall speeds in the PA-30, where it is in between them in the PA-44. This means you will often get to experience Vmc rather than recovering at a horn.
I have enjoyed flying both aircraft. The 'Nole is a great first multi trainer, but it was very easy for me to fly after doing all my primary work in the Twinkie.