Not sure about the improvements in the 410, as I have a 405CX (and only got the CX as it was cheaper than the standard 405 when I bought).
I've had a quick look on the DC Rainmaker web site and I think there's three things that would make the 410 a better buy than the 405:
1. The Bezel is improved
2. You get the "premium" heart rate strap thats more comfortable than the one supplied with the 405
3. Its a current model, so any 405 you are buying is old stock that has probably been in a warehouse for a couple of years.
The bezel on the 405 is a bit fiddly, and I can understand why it irritates people. However, I don't find it a huge problem - I just make sure I lock it when I'm raining, and accept that it won't be very responsive if my hands are really wet/sweaty. So the improved bezel on the 410 is a bonus. The other two benefits don't have a direct impact on the performance of the watch.
So the 410 is probably worth spending a little more on if you can afford it, but I wouldn't pay a lot more for it over the 405.
TBH, I dont think you'll be diappointed with either model.