My statement was "As an agent....." for good reason because of the previous sentence - as an agent you don't want an umbrella firm causing problems running deemed payments attached to SDS appeals is just going to cause pain for the agency and end clients.. Hence you may well adopt a rule of this list of umbrellas and no one else..
Now I know you don't want to hear this but there do seem to be a lot of fully PAYE compliant umbrellas (for want of a better means of differentiating between umbrellas and tax avoidance outfits) currently offering to support Expense claims and SDS appeals to attract customers. This may be because they don't fully understand the new world, it could be just doing whatever is necessary for their month end bonus..