I mean it's fairly standard practice. Whilst I don't particularly like or agree with our rather draconian benefits system and the hoops people have to jump through, I think it entirely reasonable for someone to keep their options open. As we've seen over the last few years with TfL, recruitment can easily be delayed and training courses deferred at a moment's notice. It was very clear in the advert that there would be a delay between being offered a job and starting, and any sensible person would be well advised to find bridging employment until they've signed a contract.
As said above, the training assessments are simple enough, but you do need to study and apply yourself. LUL Trainers want you to pass, but you do have to help yourself. Even then, LUL (and railway in general) jobs are some of the hardest to get, but the easiest to lose.
Finally also worth mentioning that whilst in training you will be on a training rate which is approx 80% of the full time salary. I'm not going to share the 2023 rates of pay as they will be irrelevant for anyone who hasn't already started, and those individuals will now be able to find the appropriate implementation notices on the intranet.
The 2024 rates of pay will no doubt be advertised in due course, as implementation is due to be in March for operational staff.
Apologies if I've missed anything else also - been very busy with real life the last few weeks. Apologies in advance for any delays also as I'm away for the next few weeks, although there's plenty of other helpful and knowledgeable staff reading this who do a great job of answering things too!