I tried two different cheap pens and they both sucked. Even after multiple calibrations and fiddling, you could not get the same reading two times in a row from the exact same glass of water.
I decided to just use drops, but its hard to dial in the PH really close with drops. Plus, it takes a lot of time and and its kind of a bother. Since Im going to be going hydro next grow, Because if the trouble, Ive been looking into better digital options. I also need an EC/PPM meter, so Ive been looking at those as well. I just found a good deal on a combo pen that isnt horribly expensive, but has decent reviews on Amazon. It was also recommended in a couple of hydro threads I read recently. It has a 30 day, no questions return warranty, so Im going to give it a try. Its on sale for 1/2 what it goes for anywhere else, so I jumped on it.
EDIT: I DO NOT recommend buying from that seller. He is a crook. They sent me an email saying it had shipped 2nd day air, and was supposed to arrive last Wed. It never arrived. UPS has no record of it and they have not returned any of my 4 emails. I checked their feed back (way too late) and its all negative for the least several months. Most with the exact same situation Im in. They never ship the product and dont respond to emails. I used PayPal, so I will get my money back - eventually.