A fool and his money...
For goodness' sake - why pay a company to send you back marked tests - just buy a pack of appropriate tests - the 11+ forum will tell you what is closest to the real thing in your area - get your dc to sit the test, in the correct time, in exam-type conditions, and then mark it. Then go through it with your dc and look at every qu they got wrong and find out why - have they not covered the topic yet (eg maths - much of it is yr 6 maths), did they misunderstand the qu, did they run out of time, or was it just a careless error? Then draw up a list of what you need to do to eradicate those errors, precisely, and stick to it, week by week.
In my case, I had to teach my dd yr 6 maths in 3 months, after I found out in May of yr 5 she hadn't covered most of the topics. That was the easy bit - the hard bit was getting dd to stop making so many careless errors, doing working out neatly etc - but a useful lesson for life.
I think for a lot of bright kids, because they can coast and do well without really trying, their careless errors are ignore and tolerated - I was much crueller with my dd! It was a shock for both of us - in my case how low the standards were at dd's school, and for her to realise that in the real world, careless errors wre not tolerated - I and dh explained that getting stuff right was essential to our jobs and doing it properly first time was not a needless waste of time and energy, but how the real world worked.