I just purchased a used Ko Propo EX-10 Helios and a KR-408S receiver. I need to purchase 2 more receivers. Can anyone recommend which model of receiver to purchase? I can't find any info on the differences between KR-407S, KR-408S and KR-409S, or KR-210s.

You would need to check the compability char with KO America.

http://www.kopropo.com/america/index...127&Itemid=173

I have reviewed the chart and all the receivers are compatible. I can't find any info on the differences on the 4 receivers. What are the comparisons between the $130 receiver vs the $60?

If you look at the KO site at each individual RX it lists measurements. The 409 is the fastest RX but only compatable with the 902 module