Welcome @maRAUjuana
First, DON'T PUT PH UP AND DOWN IN ORGANIC SITUATIONS.... you could, but that makes it no longer organic and a drop of it literally wipes out half your microbes and bacteria. those chemicals are stroooooong that's why a drop can make such a big difference. Rather use organic substances to either raise or drop ph in an organic grow. organic ph up = bicarbonate of soda. organic ph down = 100% lemon juice.
On the topic of the ph pen itself.... I would rather suggest getting a ph or a ppm pen respectively.
As with all electronics in life if it's a "one thing that can do it all" situation it tends to be lesser quality. I mean you can guage this off just the price, buy cheap you shoot yourself in the foot. Buy the right thing you'll only need to pay once. This is why you wont find a company like blue labs with a "one pen that can do it all". They have many different tools that can do one specific job very well.
with both the ph or the ppm you obviously never want inaccurate readings. so quality is key here..... even with quality you'll hear with the very very best quality ph probes they need to be calibrated regularly, because their accuracy swing with use. the cheaper quality you go the quicker your accuracy will go out the window.
I have heard of countless growers buying cheap ph/ppm probes just to toss them after a grow or two, because they realise how inaccurate they are and if you have inaccurate readings you'll cause more problems than anything. it's also impractical to have to calibrate a pen with every use just to make sure it's still accurate.
I got the bluelabs ph pen and the ppm pen, I use them, because they have helped me a lot more than any human has, although in organic situations every second grower will break their heads over the fact that they believe you shouldn't test your organic soil just look past those people... let them not test their soils.... we'll see who has the last laugh
I'm an organic grower and use my ph pen once a grow, sometimes I skip over it and only once every second or third grow depending on what I did with my soil before going to use it.... I use my ppm pen way more often. couple times a grow sometimes with a guarentee runoff ppm test of the soil I cooked before transplanting into final pots. I make AACT from time to time, have to test the ppm before I give it. getting into KNF will have to do a lot more testing on my side.
I would suggest BioBizz, Grow, Fish and Bloom as your nutrient line. if you think of reusing the soil in future, I would suggest keeping it alive by regularly adding microbes and microbe food. this will form a symbiosis in your rootzone and help break down any nutritive compounds that are not yet accessible for uptake through the roots, and make it accessible.
Microbes - there are many many many inoculant products, you can choose any mycorrhizae product.
Food for microbes - there are already some in the organic nutrients you'll be using, plus a good topdress of worm castings about 3 times a grow. the molasses you got there is a super food for your microbes. then look into KNF (korean natural farming) you get all kinds of microbe bombs you can make at home with resources you probably already have... Actively Aerated Compost Teas. Sprouted Seed Teas. Fermented Plant Juice. Lactobacillus Acid Bacteria Serum..... so many