Think I has seen
@PJ Diaz posting some good info on silica maybe he cant help
I personally use Armor Si right now, which is Potassium Silicate. Apparently Potassium Silicate needs to break down before being usable by the plants. The question is how much does it take to break it down to a usable form. Also Potassium Silicate will raise your ph. Agisil 16H is also Potassium Silicate, and is better value compared to Armor Si (but I got my Armor Si for free, so there's that).
Power Si is different because it's the readily available form of Si, Silicic Acid, which is why it's a lot more expensive.
Interestingly enough a buddy of mine started working for a new company last week who carries an even more concentrated version of Silicic Acid, which is also even more expensive that Power Si (if you can believe that). I had never heard of this product before, which is apparently a whopping 40% silicic acid. I can't seem to find the exact amount of silicic acid in Power Si, but I've been told that it's somewhere between 1% and 4%. That makes this other stuff at least 10x stronger, and considering that the feed rates (0.3 ml / 10L (2,64 gal)) are like 20% that of Power Si (3 ml / 5 gal), it makes this super expensive stuff a better deal than Power Si.
Anyway, here's the 40% mono-silicic acid product:
https://www.grow-genius.com/mono-silicic
Here's where you can get it online:
https://centralcoastgarden-shop.com/brands/Grow-Genius/
Here's some other good really good info about the different types of silica, and their different effects on plants in foliar applications:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6027496/#B27-plants-07-00045
Here's a summary of the above study:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6027496/table/plants-07-00045-t003/
I think the general takeaway from this study is that Potassium Silicate is great for preventing fungal infections when used as a foliar, but doesn't provide the same sort of biostimulant boosts which Silicic Acid does.