are these things legit? or just snake oil to fool the unwise

[Jet-Fighter7700]

so thought to ask here,
anybody use any of those head gasket sealer things?
like this

Blown Head Gasket Solution - Gasket Magic

Gasket Magic Solution for Blown Head Gasket, Car Overheating and Loss of Coolant Who is Gasket Magic? GASKET MAGIC WORKS. Every Time. On Petrol or Diesel. Turbos. 4x4's. Trucks. Forklifts. Generators. Racing Cars. Motorbikes. Safe on Aluminium. Since 2012, we have saved many, many...

www.gasketmagic.co.za

and this, much more expensive one.

Head Gasket Sealer | Head Gasket Sealant | BlueDevil

BlueDevil Head Gasket Sealer can be used to permanently seal blown, cracked, or leaking head gaskets, heater cores and freeze plugs.

gobdp.com

or is it just snake oil, that in reality does more harm than good, and ruins a salvageable engine, permanently

 

[Grouter]

Garbage. Pissing into the oil filler would work better than that crap.

 

[Stokstert]

It will most probably also increase your dick when you dip it into Blue Devil for 20 minutes.

 

[D tj]

This is a last resort product for when you do not have funds to do a proper fix.

 

[6spdmanual]

What car do you drive? The reviews for Blue Devil seem to be mostly older cars?

 

[Lupus]

Reading a few things, it does seem to work. Guess it is worth a try.

 

[Smugs]

It does work... It makes money for the people falling for it..

 

[Thugscub]

It just gunks up the cooling water channels.
A blown head gasket cannot be fixed with this crap.
Head off, skim, new gasket, new bolts, torque head bolts.
It's not a small job.