Used to instruct in the 300cb, mass briefing for all students on the course in the morning, then each instructor would take there four students away, two students back to back in the morning and two after lunch. There was also a 300c used for basic instrument training.
Took less time to send some one solo in the 300cb but the actual get to ppl standard took no longer than a R22, just longer to solo in the R22 because a bit more flighty and had to be sure they would lower the lever without thinking if it all went quiet, tiny bit more time in the 300cb.
The 300cb is a great training a/c but is more expensive to run and has more niggles per hour than a R22, it is a training machine, two people, solo from the right, not as powerfull as you think, three people and more power is the 300c.
Can't tell you about the 300cbi but I guess it's just like the 300cb with fuel injection, so
300cb = training a/c, two larger people only, bit more fuel per hour, bit more maintance, bit slower, bit safer for a ham fisted student/ pilot.
R22 = private owner, training a/c, two smaller people only, bit less fuel, bit less maintance, bit faster, not as safe in same conditions as above, throw away or put money aside for big rebuild at end of life.
Both good stuff but R22 will get more people through the door because it is cheaper, you can beast it day after day, it's got it's well documented problems so just learn and avoid, did I mention it will be cheaper? just look around.