The subscription model isn't great in this respect.
I travel up to a dozen times a year and backpack at least a couple weeks per year (in aggregate).
So that's 3x2x12 (3 cups per day of travel for each work trip) + 3x14 (backpacking trips). And probably another dozen or three here or there for random stuff (full-day bike rides, long drives, run out of beans @ work, etc.)
If I like Sudden, and especially if it's better than Starbucks drip served at airports, I'd use it for all of these things.
But I'm not going to+ sign up for a subscription because the vast majority of the year I'm happy with my espresso machine at home and decent drip at work. It's not like hygiene products where I just need a steady drip. My demand for instant coffee is very bursty. I expect that's true of others as well.
Maybe the logistics just don't work out without a subscription model, which is fine. And I certainly won't pretend to know what I'm talking about. But you're definitely losing one potential customer by forcing me to do a monthly subscription :)
Also, something is confusing in your ordering page. How many servings of coffee do I get for $19? I feel like that'd be useful information to have somewhere on the order page. Is it 8 cups of instant grounds? Or enough instant groups for 8 "cups" of coffee?
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+ well actually, I am to try it out. But I won't mess with starting/canceling the subscription in the future. If you gave me a way to schedule things though, that would convert me for sure, assuming I enjoy the coffee.