I'm a bit worried as I've not read very positive things about this drug. Should I be worried?
No. Remember that the leaflets that come with drugs are required, by law, to list all of the possible side effects no matter how unlikely.
Though anti-psychotics are generally not recommended for use in someone with dementia, that doesn't mean they are banned. It just means that the prescriber has to take note of the increased risk of stroke - but again, this is a small risk to begin with so even when it is increased, it is still s small risk. It becomes a question of a risk-benefit calculation and if someone is in a constant state of anxiety then that can also be detrimental to their health (mental and physical), it may also mean they may not get the appropriate level of care because what is called "challenging behavior" make sit impossible.
Keep in mind that the internet isn't regulated, so anyone can make any sort of claim they want to. Most people are much more inclined to post up negative experiences than they are positive (if a headache tablet makes you feel sick, you complain: if it just cures your headache, you're more inclined to just accept it did it's job and say nothing). There are also numerous sites that are frankly operated by cranks who make all sorts of claims without any proper evidence. Note that Wikipedia for example is made up entirely of user contributions and thus it cannot be relied upon for absolute accuracy
Anti-psychotics have also had a lot of bad press due to their inappropriate use, usually when they have been used to sedate residents of care homes for staff convenience.
The prescriber will take account of the potential risks and downsides against the benefits and make a judgement. They will also utilise the lowest possible effective dose.
Obviously if you are unlucky and worrying side-effects appear, then you'd need to report this to the prescriber or the GP and in that case it would normally be stopped.
Usually, the beneficial effects of anti-psychotics take some weeks or months to be fully evident, however side-effects can appear much more quickly. Sedation is a common side-effect and it will usually lessen over time as the person builds a tolerance to the drug. 25mg is really a very low dose; my dad was on 400mg daily and he still ended up being sectioned into a mental health unit. The safe adult dosage is actually higher than this and up to 800mg+ are not unheard of.