...but i am not sure of their quality, credit, ....
I have never heard of them before, but, there are a lot of websites I haven't heard of before.
They seem legit to me, and to be safe, you can always pay by Paypal or credit card, and have the bank back you up in case this website is scamming you.
However, I do have some concerns about these units.
What brand are these units?
Who, or where will the tech support come from?
Who are the provider of the maps?
In a few years and when time comes, how will you update the maps?
Frankly for me, I very seldom need a GPS when I am in my home town. However, this is not to say I never use a GPS at home. I do switch between 2 cars at home, and I almost always need a GPS when I fly to another city and rent a car.
So, for me, I would prefer a known brand portable unit. I can move it from car to car, stick it in my PC bag when I travel, and take it out of the car when I park in a questionable area. In addition, I can upgrade the maps on my unit easily, and fairly cheaply too.
My unit is a Garmin, but there are also a number of other good quality and well known brands too.