It's for the usual crew training and familiarisation when a new type is introduced at the moment, they now have two A21NLRs. I guess they may continue to appear from time to time but may not be the regular aircraft. Then again, others are operating their A21NLRs, EI operate quite a few routes using them and their A320s on short haul routes. The ITA A320s and A20Ns are fine - better than many European short hauls planes and the seats are a bit more comfortable than e.g. LH group but it is still 3x3 in C with the middle seat blocked.