The support that comes with the 3-pin bindings and their compatible boots is reliable, but does mean having sturdier/heavier boot options. REI does not carry anything lighter than the BC X11s mentioned above.
For the discount question, if you return an item that you purchased with your member 20% off coupon, you are able to use that coupon on a different item within the dates it is active (in this case, 11/13/20 - 11/23/20). This would allow you some flexibility with your shopping plan.
Let us know if you have any more questions and we'll be glad to help. Happy skiing!
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