Argos are not to blame
Its cheapest in argos due to;
It only having a 1 small AH battery
A slowwwww charger
The unit itself is exactly like all the others.
Argos also extends the guarantee for 3 years on it
I know someone who is on his 4th unit
Uses it every day and abuses it as well but only paid once.
As for hypo...
The WORX WG629E does have viton seals and can be used with hypo.
The seals are 100% concentrate proof resistant
The mechanism I dont know about.
A 20 litre window cleaning backpack with a chemical pump fitted. Rinsed out after every hypo job. Mine has been going 2 years with no problems. I can put you on to a great guy who supplies them no problem Des.