I have used both tablets and powder, they work the same, you choose based on your machine's instructions and what suits you.

IMPORTANT. I read another review that mentioned placing the tablet in the water tank. It is NOT intended for cleaning the machine via the water tank. It is for cleaning coffee residues/oils (i.e., cleaning the machine's shower screen and portafilter).

It can be used by machines that have a three-way valve (solenoid valve).
Machines with a three-way valve require backflush and descaling, for which two different products are needed: cafiza and dezcal (and similar products depending on the manufacturer).

Those that cannot do backflush are cleaned only with dezcal/citric acid etc., which are for scale, and are placed in the water tank.

(Additionally, since I mentioned descaling, keep in mind that some machines, due to the boiler material, do not accept descaling acids. It is better to be careful about the water you use rather than having to descale. It will be mentioned in the manual.)

In short, read the manufacturer's instructions carefully and/or ask a representative.

General summary:
machine with three-way valve: Cafiza for backflush and descaling with the appropriate product via the water tank
machine without three-way valve: only descaling with the appropriate product via the water tank

I didn't see anything spectacular after the end of the cleaning process, except that some parts of the machine were shinier than before. However, immediately after, I used the descaler from the same company. That was really worth it. The clogged espresso machine, where only two drops were dripping every thirty seconds, suddenly transformed into a machine that seemed like it was bought yesterday. I don't know if the cleaner I had previously used helped with this or if it was a prerequisite. I don't think so, though. The job was done as soon as I used the descaler.
So, try buying the descaler from the same company first, and if something doesn't go well, then buy this one.

UPDATE 14-12-2021:
I think I underestimated the product a bit. It actually does the job. What you will do is drop the "tablet" into the water tank of the coffee maker, and because it doesn't dissolve immediately, you will leave it inside even when the first fill and drain of the tank is done, and you will refill the tank as many times as needed until the tablet completely dissolves. It took me five times. So:
1) Fill the tank and drop the tablet.
2) Heat up the coffee maker and let the hot water run in doses into a basin below.
3) When the tank is empty, refill it with water, leaving the tablet inside. Heat it up again.
4) Repeat the process until the tablet dissolves. (It took me five times.)
5) When the process with the tablet is finished, fill it with plain water now and repeat the "heat up-drain-heat up-drain" process to remove the foam from the cleaner.
I hope I helped.