Personally, I've never used any special fluids to clean any of my kit .. my kit's always been
1. blower
2. micro-fibre cloth
3. "new" cotton t-shirt cut to small square pieces (easy to cary)
4. little bit of water, any bottled water is fine (don't use tap water)
For general cleaning, the blower is more than good enough. There will always be that odd flint, or grain of dust on the front lens & filter. I live with that and accept it.
For smudges, stains, and cleaning the lens (front and back), then I use the blower to blow out as much as I can; then I soak a cotton t-shirt square (one of the cuts I mentioned above) in water and press gently against the lens / filter (no moving in any direction as this may cause scratching). The moistured cotton cloth will get 99% of the smudged cleaned off. I then use another cotton t-shirt square to dry out the excess water, and a third cotton swaure to wipe it well dry. Making sure to check that there are no coars issues left on the lens / filter as I go through each stage.
For water & rain drop marks on filters, I use the microfibre cloth (only on filters, never on lenses). Add a bit of moist from breathing on to filter, then wipe it clean with the micro-fibre.
Tried many other items over the years, but found these do all the cleaning that I need. Lens pen wasn't useful at all, personally!