I would recommend an Android Tablet. I use an Asus model for passed 2 years and it is very reliable.
I see the downside of ipads is having to be locked into iTunes plus having to buy addition adapters to be able to simple use USB,s or HDMI cables which my Asus is already provided with these inputs.
But it,s all down to personal choice.
Graham I'm leaning toward android for some of the reasons you mention plus I'm more used to it as my Galaxy phone is Android based also I just have to be sure what I have outlined above for MY needs can be done flawlessly while performing.