The training of the pro will always dictate the level the product will perform. Loba products are very expensive. As soon as a pro uses it exclusively then you are working with a HIGH END pro with outstanding training. No one voluntarily works with **EXPENSIVE product if they can't get it to work. The hardener is the stuff that makes things cure quickly. The faster it cures the faster it becomes 'tough'. In theory, Loba 2K Supra AT can be used without the hardener but it takes over 1 MONTH to reach final hardness (2 coats = 30 days; 3 coats = 60 days or more). If someone believes they can make something 'go further' by mis-managing the LABRATORY produced mixture is often considered a pretender. That being said, there are MANY uses for the products without the hardener...but only the very well educated high-end pros (the one's who made it through College or University but chose to work with their hands) will grasp the subtleties of 'off-label' uses.

My only experience is with Loba products, so I won't comment much on the Bona except to say that if you have read reviews of any product yellowing over time, then I would say no, there is nothing you can add to prevent that. Be very cautious of any product containing oil, as it will yellow in time, and even some products claiming to be "waterborne" can dry down to an oil base, so read up on each product before committing. In terms of the Loba 2K Invisible Protect AT (which stands for "Advanced Technology" versus Loba's non-AT version of the same product which is still sold, so make sure you get the AT as it is more durable), the company does claim that it can be used alone to help create a natural finish that is a little lighter than other products in the lineup, but I have followed the stories of people here at Houzz who have tried to use it alone in that manner, and it generally has not worked well. In one case, someone even had to sand down a first coat of 2K Invisible AT and start over using Loba's WS EasyPrime first. The WS EasyPrime will not only prevent side bonding of the wood which could be an issue for you, but it will also help that first layer of 2K Invisible AT to go on much more smoothly. Knowing what I know about how Loba products work, I would never personally recommend anyone using the waterborne products without the WS EastPrime underneath. Is it going to darken your wood? Yes, faintly, but the wood itself is going to darken as it ages over time, and that is your REAL problem more so than which brand of finish you use. Oak, including white oak, will turn amber as it ages, and it will never be the same as it when it was first sanded and installed, regardless of coating type. If you want a lighter look permanently, you need to use a bleaching product or a whitewash product before you even start putting a top coat on to help maintain that lighter color. Another issue with any Loba product is that it has powerful self-leveling compounds which can induce dripping on the vertical stairwell risers. You need to talk to whomever your coating application serviceperson is and make certain that they have experience working with stairways with these flooring products to prevent dripping and other issues. The "2K" in the Invisible Protect AT means it is catalyzed using two parts combined right before applying. Loba claims a 10-minute working window for that catalyzed coating before it starts to set up, but I found it to be more like a 5-minute window once you lay it on, so if your provider is not familiar with working with 2K products, you could end up with a huge mess if they keep trying to go back and work that product. You have to touch it twice and move on--roll it once against the grain, then roll it with the grain and move on. For larger areas like floors, a 2K product ideally requires 2 people to keep the job moving before the edges start curing. Some contractors will be accustomed to using flooring coatings with a squeegee, t-bar type of implement to move it around, and that's just not the best approach with Loba's water-based products. You preferably need to use their specified roller to get the proper coverage. On a stairwell you could probably do some brush work, but you need a really super soft brush like a Purdy Extra Soft to avoid leaving brush marks. You can message me through my profile, and I'd be happy to talk with you in person more about your situation. I would also advise against going with the super-matte finishes. Everyone seems to want that these days, but I can tell you that a bit of sheen or even gloss is going to hold up better for you in terms of the longevity. Loba is a really strong flooring coating that should give you around 30 years of durability, but the semi-gloss or gloss may look better longer as the flooring is used, and that is true of virtually any coating brand. Also with matte, most coating specialists recommend to wait and put that on as the last coat with the gloss underneath or else you could end up with a cloudy finish. These coatings are all made to be clear, and the way that they make them matte is they add a diffusing particle in there to make it more cloudy.

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@druszky Are you certain without doubt that first layer was not some type of primer? Loba does produce a waterborne primer called WS EasyPrime that is designed to receive a topcoat layer within about 45 minutes to 2 hours of primer application. If the first layer was EasyPrime, then 30 minutes later Invisible Protect AT, then you would be OK. It's distressing to me that so many people are after the extreme matte look in coatings. First, it leads to situations like you have here where clearer coats were used first, then a matte coat used last. This retains the clarity of the coating overall but makes repairs more difficult. Also, I am not a coatings expert but have generally noticed with the amount of reading I have done this year on coatings that a higher gloss finish tends to wear better in some cases in terms of not prematurely failing. I don't know if that is because of properties that allow a greater surface resilience or what. Then, you also have the situation @SJ McCarthy mentioned, where wear along a matte topcoat can produce shiny sections. Most people selecting coatings for their homes are probably not informed by the contractors in advance about these types of issues, or perhaps more people would opt for a higher sheen.