I've purchased various pentest devices, not going to mention any names. I've always found them to be lacking in capability and storage. A better option and one where you get to assemble your own device is to use a Pi or my favourite Odroid, they tend to have more power.
Download the arm image from
Install Win32Disk on Windows
Insert a microSSD of at least 16Gb
Burn the Kali image to the ssd.
Insert into the Pi\Odroid and power on
Logon with the default account root and the password of toor
If that fails try kali and kali
passwd to change password
apt-get update & apt-get upgrade
apt-get -y full-upgrade