Colours do vary between manufacturers of both printers and refill suppliers. I don't think the viscosity is any different but may be wrong.
If you are wanting specific consistent results in colour reproduction it is better to use only one manufacturers refill ink (or perhaps recycled cartridges) as mixing may not provide what you need.
I tend to use the Universal refills as colour isn't that important and the results are 'good enough' for my needs. Sometimes kits are marked as specific because of the difference in refilling cartridges between makes of printer as well.