SAFE RACER HANS = $595
APEX PERFORMANCE DEFENDER = $549
I believe you mean Defnder :
http://www.defnderneckbrace.com/
For your $549 you get a complete system with a DefNder.
It can handle all seat back angles, is width adjustable, has the quick release built in, sliding tethers
as well as side impact tethers.
For your $549 HANS you get only a HANS to which you must add everything. Usually the low price is for the very small HANS, with another price for a standard size. To this you must add tethers, with sliding tethers extra cost.
Everything is extra cost and your total buy in to equal a Defnder is $650-$700 (depending on vendor).
I bought my DefNder at PitstopUSA for $545, with free shipping and got a $25 rebate card to use on other stuff.
For $520 I can't even buy a used HANS.
It took me exactly one practice session to get used to having it on. Yes, it does limit side-to-side a little.
But if your head is moving this much to see traffic then you need to re-evaluate your mirrors.
I did some forward test lunges and the security of having my head restrained that positively was very reassuring.
Personally, the addition of the DefNder has improved my driving as it's one less thing to worry about.