I have been a bit dissapointed in the Nikwax wash in and Spray on, as far as performance and durability.(And I use it many times a year, becasue we have many Paramo garments)
It is hard to know what is better though, since all the other brands have been changing their formulas. A few years ago, many used Fluoro compounds, and those are being pulled from the market for environmental reasons(which is good). It does mean that a brand you loved a few years back, might be different now.
I bought a few bottles of a German brand, becasue one of the German outdoor magazines ran a test of these products, and that one came out best. But, that’s maybe a bit crazy, ordering DWR from Europe
In the past I have liked Grangers.
For I uninsulated shell garments, I vary treatment. First time a washer and dryer cycle is often all that’s needed. Next time it needs a bit of love, I’ll hit shoulders/knees etc with spray on after washing and before dryer. The next time it needs treatment I’ll wash it, do wash-in DWR and dryer. Then back to just washing and drying again, etc.