Is it really broken for the users or broken is your definition of broken because that's your baby and your dreams etc etc etc? If this 25% working part represents something that users could actually use, and you are all under pressure (for whatever reason), than ship it but ship it with a plan. E.g. let the users know what's missing and what's your plan to ship the rest of the service, and possibly show them a milestones timeline so they see this is not the crappy final version of the whole thing and that you are working hard on the other 75%. That will also help with the thing about your investors by the way, I guess. Of course, that's only a very personal opinion. I have never shipped a service or product like that but as a paying user/customer I would appreciate this approach.