Have worked in both. One of the significant difference was how people in tech based roles are treated. In product based companies, tech bandwidth is one of the most important thing that product teams must work on optimising, with utmost importance given to building things only after the Product Team runs a MVP based experiment etc etc(all things you see these bhaiyaa, didis and influencers talking about)
In Service based companies, tech roles, especially coders(~80%) are considered corporate mazdoor. These are the types of companies that cause people to hate their professions. Additionally you are replaceable, because there are 1000 people on the bench ready to replace you in an hour.
Although there are cons to PB and Pros to SB as well, this has been the major difference that I saw. Do remember that most service companies are profitable, so there are lesser chances of you getting laid off, compared to product based companies or startups.