Coolant is one of things where there are just as many myths and crap products out there as there are decent ones. There is ALWAYS something cheaper that works as well as anything sold by Motul or from Honda for that matter.
The ingredient you want in your coolant, is Glycol. Whichever way you buy it. Whatever colour it is. Thats is the ingredient that works. Motul dont use magical ingredients, just glycol.
Look for either a 50% glycol premix, (Easy) or a glycol concentrate that you can dilute to 50% with distilled water. Basically the concentrate you want should have about 1000gm of Glycol per litre (Usually 996 or something), which means it is more or less just a litre of glycol. 2L of Glycol + 2L distilled water gives you 4L of coolant ready to use. At 50%.
Many you can buy are less than 50%, but only use less than that if your handbook specifies it. 33% is easy to find on the shelf, but wont provide as much anti-freeze/anti-boil protection when you need it. Dont use greater than 50% or the heat transfer properties begin to be reduced.
Anything you find without glycol in it is simply a corrosion inhibitor, not an anti-freeze anti boil, and is not ideal for obvious reasons. It wont stop freezing or raise the boil temp. It is cheap, it is crap, and it is to be avoided. Piss probably works better!
It can also be bad to mix it with glycol.
You dont need to drain/flush & refill if it just needs to be topped up. Just top it up with 50% glycol/distilled water mix. You only have to drain/flush and refill when specified in your service shedule, or if you just bought it and have no idea what is in it and no history. Dont worry about mixing brands, 50% glycol is 50% glycol.
Dont drain and refill without flushing, and dont top up with just water unless you absolutely have to, because it weakens your coolant. But is ok in small amounts.
Because of all the crap coolants and myths out there, whenever i buy a second hand vehicle i usually drain/flush and refill the coolant first service. So i know what is in there.
Hope this helps.