Actually, these lifts work great if you don't need 100% access to the undertray of a car. Doug from the NSX Files uses one, and they have swapped out the tranny on his NSX probably a half dozen times at the track using these portable lifts.
Still pricey though. Doug's portable lift was somewhere around $3.5k. Still, when you look at true side post lifts that run almost 10k, then portable lifts are far more afordable.