Most importantly, the Government receives "Government Purpose Rights" to Data and Computer Software (including source code). The "SBIR/STTR Protection Period" gives the government a copy of the product for evaluation during which the government has limited distribution and use rights. After four years, the Government has Unlimited Rights (see the SBIR Policy Directive [1]which means they have a royalty-free license to use, authorize others to use, distribute, and disclose said data and software for Government purposes. All of this is defined in the model contract [2] for Phase I and Phase II awards. There are some restrictions, but you'll need to read the documents carefully to determine when these items apply and/or can be excluded.

With that said, I've found SBIRs to be exceptionally useful for my business (I've won $750k in Phase I funding and administered $1M in Phase II funding). The proposal forced me to hone my idea and I received feedback fairly quickly (6 months) with a week or so of invested time. The product is built with minimal risk to my business and the Government can set up meetings with potential users (something that is exceptionally difficult if you aren't on contract). Lastly, with most SBIRs you can request up to $10-15k of additional funding for Commercialization Assistance which permits you to sit down with an adviser who can guide you on bringing your product to market. SBIRs are really an ideal method for Small Businesses to grow.

[1] https://www.sbir.gov/sites/default/files/SBIR-STTR_Policy_Di...

[2] https://www.acq.osd.mil/osbp/sbir/sb/resources/model-contrac...

Edit: fixed links, added statement about my involvement with SBIRs.