Does a provisional patent application allow us to present our tech publicly?

Yes, a provisional patent application effectively provides you with "provisional protection" from someone stealing your invention because once you have filed your provisional application, you immediately have the earliest filing date for that invention which you may subsequently disclose to third parties - in other words, if the third party or parties filed a patent application with respect to your idea, under the new AIA, which converted the US patent system from a first-to-invent to a first-to-file system, your earlier filed provisional application would have an earlier filing date, and therefore senior rights, than the later-filed third party application. Your application could effectively be used as prior art to prevent the third party from obtaining a patent. Note however that a provisional application will in and of itself never lead to a patent and patent protection in view of the fact that a provisional patent application is never examined - you will need to convert the provisional application to a non-provisional or PCT application within one year of filing your provisional application. As for investor's "take" or "rights" to the patent application and any subsequently obtained patent, that is within the realm of whatever you and inventor agree upon in view of his investment.

As further remarks in connection with the point noted by Bart, note that ideally a provisional patent application should be as complete, accurate, and thorough as a non-provisional application just to avoid the point noted by Bart. For priority to be valid, whatever is disclosed within your later-filed non-provisional or PCT application, should be in your provisional application such that the provisional application can in fact provide priority for the later-filed non-provisional or PCT application. If further developments are in fact developed, then the appropriate procedure would be to file another provisional application incorporating in it everything that was in the first provisional application and then adding the new development - in this manner, nothing ever gets "lost" or "forgotten" and again, your priority will be fully protected. Just note further that your non-provisional or PCT application needs to be filed within one year from the filing of the first provisional application.