The advice I have found so far indicates that you need product liability insurance if you "make a change" to a product (even if you are not the original manufacturer). Is adding software is a sufficient change to warrant needing insurance?
I'm not an attorney but I am in the IT industry so will answer based on what I know.
With your question about Products Liability Insurance - Typically anyone who manufacturers, distributes, imports, exports and even sells high risk products should consider getting a Products Liability Policy. With that said, unless you feel that there would be a reason that someone could make a claim against you then I don't really think you would need Product Liability Coverage. Loading software onto a tablet and selling it does not seem like "high risk", but I guess it depends on what type of software you are installing.
What you may consider looking into is what is called Technology Insurance. This special type of liability insurance is designed for IT professionals and people who work in the tech industry.
Again, I'm not an attorney so you may want to consult one to be sure based on your type of business.