Last year I installed a 5-gallon accumulator tank in my 5er and couldn't be happier with the results. I was able to install it in the space under my refrigerator, adjacent to where the water heater is located. Other than working in a confined space the installation was pretty straightforward. I installed a tee in the 1/2" PEX cold water supply line to the water heater and tied the line from the accumulator in at that point. I used metal fittings and copper crimp rings. The original plan was to use Sharkbite fittings but they all leaked during a 24-hour pressure-test period. My tank has a 3/4" MPT outlet to which I attached a 3/4" x 1/2" reducing ell, then ran 1/2" PEX to the tee in the cold-water supply. A 1/2" brass ball valve installed between the tank and the tee allows me to isolate the pressurized tank when we are underway. It is just a "nice to have" addition.
In use, the tank performs flawlessly, evening out pressure pulsations from the water pump, especially during low demand requirements such as light hand washing. My wife and I both like the fact that we can flush the toilet a number of times before the pump comes on - very much appreciated at night since we are both relatively light sleepers. I also like the reduced pump cycling. Our tank has a 2.6-gallon draw-down before the pump kicks in.
Good luck with your installation and if I may, I would recommend at least a 24-hour pressure test of your system prior to use.