Are these pH pens reliable?

Not sure, i paid 44€ for my ph pen, i know there are a couple for 10/15€ but i would assume that a 3k€ car to not be as safe as a 22k€ car whenever they crash. I can't know about those from experience but if you calibrate and they still give out different readings of the same solution- 1° there may be different density nutrients mixed into the water and as u split it into 2 cups one gets more of the less denser liquid and vice versa. 2° the ph meters may just not be reliablr, but you can use those as if it was a wife and a mistress, each with an opinion but both probably wrong. 3° you can not really care about 0.5 of a missreading because if you feed at a value where both of those read the same liquid as a value inbetween 6 and 6.5 then you are more likely for the value to actually be in that range. Stay lit and grow good shit growmie.