Thermally, your unit will supply water at 26 LPM with a 20C rise which = 36.28 kw, so to get water at this temperature requires mains at 30C?? if i am interpreting what the brochure is saying. Also the fuel input is 55kw (199mj/hr) so efficiency a pretty low 66%.
If one uses a average mains temp of 10C then that unit will deliver 13LPM at 50C. or with a showering temperature of 40C, 17.3LPM or just over 8.5LPM to each shower, so unless there are restrictors fitted to reduce the flow to 8.5LPM it just won't work, even using one shower then its still 8.5LPM except you install/remove the restrictors constantly for 1 or 2 shower operation. (8.5LPM would be perfectly acceptable to me)
A 36kw combi will deliver exactly the same flowrates (more efficiently) so except that one doesn't like the complexity of a combi or is heating the house by other means then I can't see any benefit.