NI has been royally stitched up in this Brexit agreement. Take pesticide regulations; we have unfettered market access to GB for treated products, i.e. all conventional food, from NI. GB food flowing into NI must comply with EU regulations. Imagine there's a new, safer, less persistent OSR herbicide that is authorised for use in GB, but not in the EU due to a mixture of incompetence and bureaucratic inertia (just like the Covid vaccines); we cannot sell our honey to NI, growers in NI cannot use the new herbicide, but it's OK for us to import stuff using a older more dangerous product because the EU says so. The EU has control, but the people of NI have no way to influence that control.
Maximum Residue Limits for pesticides in food in GB are likely to diverge from those in the EU, as science develops. What happens when our limits become lower than those in the EU? And it's highly likely that is the way things will go; with only GB to think about, our regulations will become tailored to our needs, not diluted by the needs of the Spanish/Greeks/Estonians etc. So, we (GB) can sell to NI, but NI cannot sell to GB. How is that an example of a United Kingdom?
OK, let's get rid of pesticides altogether. Same thing applies. A product classified as organic in GB may or may not be accepted as organic in the EU. Who decides for NI? The EU. The organic control bodies in NI (like in the rest of UK, these are private companies without government oversight) can comply with EU rules if they want to label their products as organic, but EU organic farmers are permitted to use sprays that GB organic farmers are not. So is 'organic' food from NI really organic? Follow the wrong set of rules in NI and you can't sell to GB.
I guess that we could say this is all a natural consequence of not wanting a fence along the border, and if that's what the people of NI regard as their priority, then so be it. It helps that most people in GB couldn't care less about NI.