When designing and developing a user experience, how much weight should be given to matching its qualities with those of existing products, support and service from the same organisation?
There are many aspects to this question, and the answer will depend on specific of your project. However, here are some things to consider:
Will the user ever interact with any of your other products? A company might have multiple products targeted to very different users and those users might never be aware of the existence of the other tools. In this case, I would argue that it’s ok if the ux varies and is optimized to each of the user’s needs. However, if you have multiple products used by the same user (e.g. Word, Powerpoint, Excel, etc) they should all follow a similar ux and behavior. Otherwise your user will get frustrated learning new skills for every product of yours. Think of the last frustration you had when a feature in Word did not behave the same in Excel, or a behavior in Photoshop vs Illustrator.
How important is branding? If both products are completely different, you want to at least keep some branding (logo) and color use resemblance between them. Just as a courtesy to your user for them to recognize your product and relate your brand values to the capabilities of this new product. It adds a layer of familiarity and comfort using a new product made by the company responsible for a product I used before.
Support and service are critical. Support and service exist at a company level, not at a product level. Support for Photoshop should not be different from Illustrator. The user expects the same level of care for both, since speaking to a Support agent is interpreted as speaking to the company. Therefore, Support and Service should be consistent because the company portrays a consistent mannerism.