Some clarification of Yakima kayak carrying nomenclature:
A "saddle" is a mount that supports the kayak's hull on both sides. Yakima's are two pieces per bar, one for each side of the hull. When looking at them from the front/back, they look basically like a "U." The kayak sits in the saddle like, well, a saddle. Saddles are very secure, and the boat is generally carried upright (hull side facing the roof of the car). Downside to saddles is you can only carry 1-2 boats on your car, depending how wide your roof/bars are. On my OBW with 48" bars I can only get one kayak. On my Isuzu Trooper with 60" bars I can get two.
A "stacker" is a vertical bar, which allows the kayak to stand on edge and be lashed to the stacking bar. I believe this is what Subaru offers as an OEM part. Advantage is that you can fit multiple boats on a smaller rack/roof.
A "roller" is a sort of saddle, but it replaces the fixed saddles with rollers/wheels that allow easier loading of a boat from the rear. Usually a set of rollers is used in the rear coupled with a set of saddles in the front, to make loading easier. I have this setup on my Trooper, as it makes loading the boat on the high vehicle easier. It's not really necessary with the lower roofline of an OBW. On a Forester it would be a toss-up.
A "tower" is the part that clamps onto the car's roof, side rail of existing rack, or rain gutter (I'm showing my age here). All of Yakima's current towers, including the one designed for the Forester, are lockable as far as I know. They require the purchase of optional locking cores.
Best advice? Go to a local reputable outdoor store that carries both Yakima and Thule and get their advice for your car. My suggestion, as a former manager of an outdoor store that carried both, is that Yakima is a better product (IMO). If you have a fiberglass or Kevlar kayak, then I'd highly suggest using a saddle system to protect the finish of the boat. If you have a plastic boat, then any mount will work. But, I still prefer saddles for ease of loading and stability.