Good, deep, accurate machine. As always it will benefit greatly from the purchase of a DD coil. They're not fast, but they don't miss much in the hands of anyone that takes the time to learn it.
The 505 only has 19 tones. It's the 705 that has 28.
And the toughest part for new users is GB, because unlike other machines the Xterra series GB numbers are higher for low mineral compensation, and the lower the number the hotter the soil conditions.
Randy's book (Understanding Your Xterra) is the single best tool you can get to cut the learning curve. It's easy to read, so read it twice. Then go back to it after each hunt until you get a good grip on what you're experiencing in the field.