I suppose you wanna check the Wi-Fi availability/speed because you have a Wi-Fi enabled laptop/PDA. If that's so, why do you want to buy a separate device just to check the connection availability? Your laptop/PDA can show you that info.
But if you don't have a laptop/PDA and want to check the availability of a Wi-Fi connection just for the heck of it then you can buy one of these devices.
Hope that helps.