Fish Tank 'disinfectant' Type Cleaner

I haven't come across that Interpet product so I know little about it.

When my last but one betta died of lymphocystis I sterilised everything in the tank to be on the safe side then fishless cycled it before getting another betta. I can't remember exactly what it was I used but it would have been either cheap basic range supermarket bleach, the thin stuff that costs less than £1 (no perfume, detergents etc) or baby bottle sterlising solution. Supermarket own brands are cheaper than Milton.
After using these you do have to rinse very thoroughly then rinse with water overdosed with dechlorinator. It is worth soaking things like nets and silk plants in over dechlorinated water for a few hours to allow it to penetrate into the fabric.

This is probably over the top, but I was happier doing that than risking another fish in the same tank.