I recently completed my third? winter off season with the Speedstroke Gym. Great machine. Pricey, but less than the price of a new ski in the US, and it will last much longer.
Listening to podcasts on earphones or watching videos is the best way to pass time. Moderate intensity or high intensity intervals really helps pass time, too.
Like Greg said, it's a very efficient way to get in a paddling workout before or after work if your life is scheduled tightly with family and work commitments. I'm on mine about 4 days a week in the winter - 45 min to 90 minutes at a time.
I completed the Molokai race last month having paddled on water only 4 times in the preceding 8 months - just Speedstroke Gym paddling - and I finished in a respectable time. Not proud of all that erg paddling, mind you, but when free time is limited . . . Erik Borgnes