You get what you pay for... The pumps in sex shops are toys...
I prefer vacutech they make a great product
And frequently dangerous toys!
I've seen high-quality pumps in a few higher-end sex shops, but most are junk.
It is essential to have an accurate pressure gauge and a pump that increases pressure by predictable and gradual method. I cannot stress this enough. It is very, very, easy to go over the amount of pressure that's safe for your penis. In fact you will likely get to the starter pressure of 3.5Hg and barely feel it. Your instinct will be to increase pressure to the point just before it's painful and that is far, far, above what's safe. You won't see or feel the damage immediately either. When your penis turns purple and your inner foreskin swells and you find your penis sore and edema-filled, you will likely have already put your pump away. Over pressure can lead to medically damaging complications including ruptures of blood vessels, nerve damage, skin and mucosa damage, and erectile dysfunction.
Don't buy a pump unless it's a good one and then follow the rules. PE is safe when you follow the guidelines. It's like skydiving, car racing, mountain climbing, weight-lifting, or any other inherently dangerous pursuit. You can seriously and permanently injur yourself if you do not follow the safety guidelines.