Looking at the Skimlinks FAQ, it can be removed quite simply, so if the experiment (I assume it is an experiment) is not successful then Mumsnet Tech can remove it.
I feel we all need to remember that we do not pay to use Mumsnet. Mumsnet must need quite a bit of income these days to keep operating and thus I am not surprised that Mumsnet is looking at and testing various advertising income generation methods.
When users like myself post links to other sites, in the past Mumsnet does not make any money if someone clicks the link and then purchases something from that company. The skimlinks system looks to me to be trying to solve that issue, by creating an affiliate link when possible.
If Mumsnet stopped us from posting our own links to other sites I feel that would devalue the usefulness of Mumsnet as a place to provide Parents with information. So having Skimlinks in place may be the price we pay for being unrestricted in our ability as users to link to other sites.