I've been looking at various Aluminum options for my deck. Most recommend flanged posts surface mounted. Make sure you get railing satisfying code. Some railing companies sell products that are only legal on front porches and other applications of less than three feet off the ground. (too weak or railing spacing with more than 4" gap between ballisters)

Flanged posts which are welded aluminum are weaker than those formed in one piece(Harder to find and more expensive). Thickness and alloy used affect strength as well as thickness of post. A cover plate to hide the screws holding the flanged post thru the deck would be nice.

Some are assembled on site (lots of labor), others are shipped as complete sections(hinged rivets allow bending section for stairs. If you have steep stairs be sure that ones ordered have a stair attachment option that allows the stair angle you have. If you have horizontal turns that are not 90 degrees, make sure the vendor has hinge options that allow mounting rail to the angle.

I am looking at Gilpin Summit series. Prebuilt sections. You can cut as needed. Swivel kit allows flexibility for stairs and sideways angles. Be aware that ideally, you want to build a wall with all posts evenly spaced. Custom made rails can do this perfectly. If you want to achieve this level of perfection with premade pieces you will have waste of cutting down longer segments. You especially want to avoid the situation of 6' segments with a 1' end segment to make up the length required. Summit series covers rivets on ballister to rail connection, but provide no covers for screws on rail connection to post or for screws thru flange plate on posts.