[@Lord Wraith]
The only drawbacks to being transformed all of the time are story-based. He doesn't taste good food, he doesn't get the satisfaction of a night's rest, he can't properly feel the touch of another person. Stuff like that. Tactically it'd indeed be best for him to stay transformed permanently, he just doesn't want to.

In transformed state he is indeed stupendously tough. However his ability to actually inflict harm usually isn't all that increased. At worst he's going to be punching with the force of a baseball bat to the face. Threatening to a normal human, but not exactly a threat to most of the superhuman characters. So I figured his durability is fairly balanced. Besides, if he's full-on made of steel you can avoid him by climbing up a ladder. Rungs won't hold the weight.

And no, he doesn't get extra superpowers. As the rest of that paragraph implies, the different 'powers' gained are the properties of materials he's mimicking. If he's made of glass he's hard to see. If he's made of paper he's incredibly light. If he somehow manages to become uranium he'll give people radiation poisoning. That paragraph is to indicate that he can gain access to the properties of a wide variety of materials, to a wide variety of effects.

I chose 1.5 seconds because it's fast enough to easily do before or after a fight, but not usually during a fight. One point five seconds is the time it takes for a human to cross a 5-meter gap and shank you in the spleen. If you think that's too fast I can slow it down.