Treat the offer with extreme caution as what they are really saying is, "we'll take your money - why wouldn't we - but you don't have a job waiting at the end of it".
Considering the unlucky applicant will have paid for the second day, then would it not be prudent for the hopeful to return for that second day should their test scores have been sufficient to meet their APP criteria, and they aren't travelling from Outer Mongolia?
Afterall, if the plan is to apply again next time, then you cannot really put a price on experience of assessment processes.
I do, however, echo what you say regarding going down the non-mentored route.