I had the same question and summized the following;
the 407 has a "standard" ariel so needs a longer ariel tube
the 408/409 have a special "co-ax" ariel and so don't need as much ariel showing
This was the response from KO America:
Toby,
407 - regular copper stranded wire antenna
408 - coaxial antenna for better range (discontinued)
409 - coaxial antenna for better range
Here is the compatibility chart from our website for the response modes
http://www.kopropo.com/america/index...127&Itemid=173
Regards,
Robert Morris
KO PROPO America
[email protected]
Tel: 310.532.9355