Whether the appeal was admissible despite being filed without conclusions or motivation and without a later brief
No. A declaration of appeal without motivation had to be supplemented within ten days of receipt of the challenged decision; because no motivated brief was filed in time, the appeal was manifestly inadmissible.
Under Art. 425 CPP, a bare declaration of appeal must be followed by a motivated brief within the legal period. As the appellant received the full decision on 2010-03-10 and filed nothing further, the court could not enter into the matter and had to reject it preemptively under Art. 431 al. 1 CPP.