The simulations for linear devices using the 3D Monte-Carlo code ERO have a number of particularities of both physical and technical nature. Many physical effects introduced and tested for these simulations (elastic collisions, population of metastable states, etc.) can be relevant for tokamaks as well. The current status of these activities is summarized. As an example some simulations reproducing the experimental observations at PISCES-B and Pilot-PSI are presented. Main deviations and ideas for their origins are discussed. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.