When I was looking at alternatives to Siebel I remember emailing flavour-activ to see if they had anything suitable for small level craft beer enthusiasts. Unfortunately they never responded so it is good to see that they are now open to that market.
The uno kit is very good and very shelf stable (siebel is not and needs to be used ASAP). The siebel kit also contains a number of flavours that are quite rare including goaty (fascinating but I've never actually encountered it in any commercial or homebrewed beer). 69 GBP is a good price considering how many taints you can do - if you don't have a large group, you can mix up what you need and store the rest for between 9-12 months. Can't do that with siebel (you can store, refigerated but have much less time before the flavours dissipate). Additionally, there are no postage costs for aroxa - 69 GBP is the total price.
Main issue with the aroxa UNO is that it does not contain some of the very common ones, including acetaldehyde. We had a taint session at my brewclub and I had to order separate acetaldehyde, adding to the overall cost. They are easier to use than siebel though and the shelf life is important. UNO was the affordable one I was referring to earlier.
As mentioned above -any group booked in to sit an exam is eligible for a free siebel kit (you pay postage) from the BJCP but despite confirmation of contact from Kristen England at BJCP, I never heard anything further from our enquiry and had to order directly from Siebel instead.
The two major things you need to do to do well in the exam have been mentioned so I will just reiterate - taste and evaluate as much beer as you can and learn to describe what you taste in the appropriate language. Be as descritptive as possible, don't make stuff up and align flavours with causes (especially in relation to faults). Make no assumptions about how the beer is made (kit, grain etc) and use qualifiers such as 'if mashing, mash at a higher temperature for a more dextrinous, fuller bodied beer'. Write some judging sheets, volunteer to judge at a comp if there is one between now and then.
Setting up taint sessions is a great way to attune your palate to particular flavours and learning how to describe those. Remember you may, as an individual, have higher sensitivity to some and higher tolerance/thresholds to others.
Knowing the guidelines is important but having a decent understanding is sufficient. Being able to describe and elucidate is more important although you don't want to cane a bo-pils for a touch of dms but suggest it is acceptable in a dortmunder.