you can scarify/aerate lawns at any time although in my experience the response is generally better in spring as the grass has time to re-establish over the summer before you get to another wet winter. However I would not do it while the lawn is still squelchy as you'll compact the soil by walking over it which may cause it to not freely drain thus encouraging more moss in the wet areas.
can't help on the aldi/lidl questions tho as I do mine the hard way - with a rake and a fork!
