We sent DD1 to 3 year old kinder, now at 4 yo kinder and she will start prep next year at 5. (She turns 5 in 3 weeks)
She was reeeeally ready for kinder, thrived and loved it. She went 3 full days a week and for us, it was worth the money we paid to send her.

I personally think 3yo kinder is great, many others don't, I think it comes down to your child and what you think is best for them.