They're fine. I use Animed direct as they usually work out slightly cheaper for what I need but it varies from med to med. Vio vet and vetuk are good too but usually a bit more expensive. I know a lot of people and a rescue who use Pet drug or Animed for prescription medication. You just ask the vet for a written prescription and it should last for 6 mths worth if its something they will need long term.
Prescription flea spot ons like Advocate and wormers are massively cheaper, just do the same and ask for a prescription. I got a 6 pack of Advocate for considerably less than I could get a 3 pack from my vets and the crazy thing is that CVS vet group own Animed and my vets were owned by CVS.
Vets usually make a small charge for a written prescription but in my experience the meds are half price online.