Re: Aikido - Is there Randori? Is Aikido a Workout?
I will leave the discussion of Shodokan/Tomiki style to people who know it better than I do. My experience is with mainstream Aikikai.
To answer your questions in general, aikido can be a good workout (it has been an important part of my workout regimen, which has melted 30 pounds off me since last autumn), but is generally less strenuous than judo. There is randori in aikido, but the purely defensive nature of aikido makes it necessary even in randori for one participant to take the roll of defender while others take the roll of attacker. Also, aikidoka generally don't get to do much randori until they have some experience under their belts.
Aikido is unlike tai chi in that participants practice their techniques on real people pretty much all the time (except for weapons kata).
A lot of people come to aikido from judo. One of my instructors, in fact, was a judo black belt before coming to aikido. He says it was a pretty smooth transition.
Hope this helps.