Pumps like Bathmates well give you temporary girth increases. The longer you do it, those gains become permanent. But! It is very slow. I've been using mine for over two years, along with jelqing, I've managed to only solidify between a half inch and 3/4" girth gain.
The temporary aspect is fun though. She can definitely feel the difference. I pump every other day for 20 minutes, medium to higher pressure. Just remember, you can do damage if you go all at it 100%.
You need to make sure you have the mindset that it's a marathon. Treating it like a sprint will kill your EQ (erection quality), and give you all kinds of blood spots and stuff.
Just do your research and start with jelqing. It's easy, and you can really get a feel for how much your unit can handle. Feel free to PM me if you'd like more info.