If buying second hand be wary of memory issues that mean you are limited to the amount of apps you can load on to the device. Some slightly older android devices (jellybean os) can run out of usable memory with only 2 or 3 apps installed. Apps have grown massively in size in the last 18 months. I have an 18month old tablet running jellybean which was my sons which quickly became useless due to the above problem. I believe rooting the tablet would help with this but as it is a 'generic' model rooting support is non existent so you are basically screwed. I would recommend getting at the very very least 8gb of system memory and android version kitkat which kind of handles memory in a more sensible way. The 18 month old tablet has plenty of space left for files and photos etc and a 32gb memory card with films on etc but it only allocates about 500mb of memory for app installation and the same for the operating system. Some games are 200mb large and coupled with facebook (approx 85mb) youtube (approx 35mb) netflix (approx 40mb) see where this is going? I have bought my son a new tablet from a known brand with more memory and later android version and it handles the above problems in a sensible manner.
PS I don't know much about these issues, just what I have learned over the past couple of years from my own experiences.
Shout up if you need any more info.
PPS. Well known brands of older tablets will probably handle the above issues better too as my 2 year old Galaxy S3 phone with 16gb memory has had no issues and still going strong (albeit in my sons pocket now).