Explains the 3 types of red dot sights.

I don't use anything less robust than holosun on my firearms, bar testing.

You can get lucky with some cheap amazon/aliexpress/wish red dots but they can, more likely than not:

Come loose,

Not hold zero,

Lacking range in brightness adjustment,

Imperfections in the visible dot due to poor manufacturing/QC,

Be incapable of being zeroed due to lack of adjustment,

Not be purged properly resulting in the internal lenses fogging.

And at the end of the day they just are not robust because they are built down to a price rather than up to a standard.

I did buy a cheap amazon RMR clone to test on a pistol before getting a decent sight for it to see whether dots on pistols were worthwhile and for that purpose it was ideal(30 quid to try a concept vs 300), but having swapped it out afterwards the difference is night and day.

But to answer OP, within 50 yards dots are streets ahead of iron sights for practical purposes(ie not bullseye). Simply not having to align your irons over the target before shooting cuts out so much wasted time. Similarly scopes with any magnification are going to be slower than red dots. And as a side benefit, if you are bringing a new shooter out to the range(which we should all be doing to grow the sport, hearts and minds and all that 😉) there is nothing simpler than just telling someone unaccustomed to firearms to just put the dot on the target and that is where they will hit. Completely cuts out any sights related explanation that would otherwise be needed with irons.

With a bit of practice and knowing your holdover you can hit steel plates at 300 yards with a dot. Even easier if you stick a 3 or 5 times magnifier behind it.

If you want to try one out then get an amazon or similar quality to test.

When you want to upgrade it get a holosun or a vortex sparc ar(former have a better range of features, latter has a better warranty).

I have 3 holosun dots and 1 holosun oem rebranded dot and I will buy holosun again if I need another.

Alternatives of similar quality are primary arms, vortex sparc series.

Holosun's eu site(they have good black Friday deals):

https://www.holosun.eu/en/

Optics site with a good range of everything, including dots:

https://www.optics-trade.eu/en/

Depends on the vermin size more than anything.

If its mice or smaller I'd opt for something magnified, because of the small size.

Rats and larger yes, dots are very effective.

Obviously your mileage may vary depending on eyesight, size of vermin, undergrowth for concealing the vermin, etc.

Well, assuming you have a standard picatinny rail to mount it on, this is a very cheap and basic dot from Holosun:

https://www.holosun.eu/en/p/70127379

I have that model, currently on a 22lr rifle and before that on a 12g shotgun and it has stood up to a significant amount of wear on both, and the recoil of the latter with no issue. It is about 4 years old now and never changed the battery either(shake awake feature turns off the dot after x minutes of no movement, and has a massive battery life to boot.

If you are looking for a very basic but very robust model, go with that.

If you are looking for a tiny dot more suited to a pistol or maybe a shotgun and want to try it as a concept for cheap, this is the RMR clone I bought from Amazon a while back:

https://www.amazon.co.uk/FIRECLUB-Airsoft-style-Micro-switch/dp/B0773G4P53/

It is far from perfect(but did hold zero to it's credit) and if you like the concept I would upgrade to the holosun linked above, but if you want to try out the idea before investing a couple hundred in a better dot that is one I can recommend.

Then you'll need an adapter for 11mm to pic rails, along with the whatever dot you go for. Picatinny rails are the standard for dots bar pistol oriented dots which have their own own mounting systems(footprints).