Personally, I choose to use 2-bath fixing, made easier by having the fixer sitting permanently in a Nova vertical slot unit.
Do not exceed the capacity of the fixer
Residual silver depends on fixer usage. There are three ways of keeping the residual silver to acceptable levels.
1 Fix only a few prints before replacing the fixing bath (approximately 10 20.3x25.4cm (8x10inches) prints in one litre/US quart of working strength fixer).
2 Use two-bath fixation.
3 Use a single fixing bath plus a washing aid. The number of prints through the single fixing bath can be increased to approximately 40 20.3x25.4cm (8x10 inch) prints per litre/US quart of working strength fixer.
The two main reasons not to use 2-bath fixing are space/convenience and up-front cost. It obviously depends on the quantity of printing done.
If cost is a main issue, it's often suggested that simple fixer (sodium thiosulphate plus a little sodium sulphite) be used as the second fixer bath*.
If it is correct that Ilford's claim that wash aid (mostly sodium sulphite) is a suitable second bath, then perhaps an economical second bath that might be better would be a dilute simple fixer (maybe a handful of sodium thiosulphate and a spoonful of sodium sulphite) to a Litre of water. The downside would be that it wouldn't be suitable to be promoted to first fixer bath when the used first one is discarded.
* simple fixer might be better if one is tempted to go straight to selenium toner without a rinse.