I agree that you can cut one of your featherweight bags to just accept the tip. I like the stability of the coupler myself.
When I started my Wilton courses, I purchased 2 of the large couplers. I have NEVER used either one and probably never will. I use disposable decorating bags 95% of the time. Just cut the appropriate amount off the bag and slip in the 1M (and other large tips). You don't need a coupler.
Here is a link with information and a video on how to cut bags, use tips, and the difference between featherweight and disposable:
How to Choose and Use Decorating Bags
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