Why would I want to use your company for buying an I-Bond myself? Treasury Direct kinda sucks, but it's really not that bad. And once you're through the initial setup repeat purchases (like each subsequent year) is a lot easier.
Why would I want to insert a middleman into a long term investment? If you all go sideways -- which is incredibly likely within the next 10 years -- then it'll be far more hassle than the up-front TD signup irritation.