Now that it works fine I have programmed it and played around with it. It does seem to do all I wanted and more. Certainly useful for the sort of diving I do and far more flexible than tables.
I am just worried about its flakyness when I got it out the box, changing the battery made it worse and then the next day and since despite trying it every now and again it seems fine.
For something I am wanting to take to 60+m and rely on I am still wary so will see what Delta P say tomorrow.