Positional aids are simple devices meant to discourage rolling onto the back. What they can reasonably achieve is worth understanding first.
How they work
By making the back-sleeping position uncomfortable enough that you move without fully waking. That is the entire mechanism — it is behavioural, not medical.
Give it time
The first nights are usually disturbed while you adjust. Judging one after a single night is judging the adjustment period rather than the device.
The rest of the bed matters
Side sleeping needs pillow height that keeps the neck in line with the spine. A trainer that moves you onto your side while the pillow is wrong just swaps one problem for another.
When to seek advice
Loud snoring, gasping or daytime exhaustion are worth discussing with a doctor. A positional aid is not a substitute for that conversation.