No need to seal is an amateur mistake, no need to feed yes, but the top layer still needs sealing, hence why leather was stained in the first place.
Gliptone twins aren't the best imo. The cleaner is somewhat rubbish at anything other than very light dirt and the conditioner softens the leather but also attracts dirt.
Basically dodo juice leather cleaner (tried and tested, similiar performance to Dr Leather advanced cleaner but much cheaper) and the dodo juice sealant is enough. However, I can't see why you can't use a conditioner under the sealant to soften it and not attract dirt.
I've written a whole guide on this in the detailing section if interested