Bought this because the dual plastic plungers on the four toilets in the house have all cracked and broke. I went for a single flush just for the robustness of the plunger (still the same plastic, but expect to last longer). I was expecting to have to remove the cistern to install as I didn't know the make of the existing unit. I was pleasantly surprise when I gave the base of the existing unit a 1/8th turn and it detached from the support mechanism and was completely compatible with the Storm 33A - I would definitely recommend trying this before going to the hassle of removing the cistern. Installing the Storm 33A, therefore, took little more than 15 minutes. Now going to buy 3 more for the other toilets.
BTW my instructions were in French too but I easily found the English version on the Siamp website.