Everyone has to make the decision if it will do what you want it to do. A few dollars doesn't make a difference in the long run, if you are happy with your choice.
I have had my 505 for 16 months with no problems and it does exactly what I need it to do. It fits my needs perfectly. If something happened to my 505, I would want to find another 505.
There are a lot of posts about the 300 vs the 505 and from what I understand, the clarity is the same and screen is a bit smaller. check
this thread and
this thread.