Thoughts on this reti opening line?

It goes like this: 1. Nf3 d5 2. c4 d4 3. b4 nf6 4. bb2 c5 5. Na3! The point being after 5. cxb4, black leaves the d4 pawn very weak and white can attack it with either nb5 or nc2
Some quick analysis:

Declined with e6:

Thoughts on this reti line? Is it sound?

It seems rather interesting and not too hard to get given nf6 is quite common at 1500's level after 3. b4. 
4. c5 is pretty much the only good move for black in that position and 5. na3 looks like a rare move so it may confuse the opponent, but given the lines it seems to be it gives white good positions after 5. cxb4 so probably black does a better decision by not taking the b4 pawn

I agree it gives white good positions after cxb4. White incites black to play cxb4 removing the only pawn defending that d4 pawn and leaves it very weak

Yeah, black should decline the b4 pawn and play either e6 or nc6. 
The only game in the masters database on lichess shows a6 was played but i doubt anyone online would play that move

Thanks for the feedback 
I'm using it next time i get to play the advance reti as white, assuming black plays c5 after bb2

the second diagram just loses a piece for white with 10.Bg2. Better may be 10.e3

It doesn’t.

If black plays 10. Bxf3, after 11. Bxf3 the rook on a8 is threatened so black can not capture the knight on d4

you are correct. white drops the c pawn.