I use a Blue Lab pH pen as well, I use a couple cheap-o’s for my ppm meter. The first cheap one I bought lasted forever and did it’s job accurately so I never felt the need to invest in a high quality one. I cannot say the same for the cheap pH pens, I definitely recommend investing in a nice instrument for checking your pH. I picked up my Blue Lab for about $90, but whatever one you get make sure to buy plenty of calibration and storage solution to go along with it.
pH liquid color indicator, and paper test strips work as well as any cheap pH meter. As far as TDS, just use your nute makers schedule and watch your plants. I rarely use either, but I am growing in a well buffered media.