Giggey,
Just out of couriosity, what is your company minimum alt sel to use OPEN DES?
How low is your
A320 OP DES at low altitude
The only limitation I am aware of is at FCOM 3.01.22 Page 1:
Use of AP or FD in OPEN DES or DES mode is not permitted in approach, unless the FCU altitude is set to, or above MDA (MDH) or 500 feet (900feet for A321), whichever is the highest.
Also intercepting G/S from above is not recommended in OPEN DES.