How important are internal frame reinforcements?

So I recently noticed CoolCat sells reinforcements for internal frames. Apologies if this is a newbie question, but how essential are these things? At least to my amateur eye, Dollfies don't strike me as particularly fragile, but given how expensive these things are, I wouldn't want to take chances if internal breakage is a thing that plagues DDs

They're by no means vital, but if you like to play with your girls a lot and often change leg/arm poses that put strain on the shoulder and hip joints, you may want them. Simple as that, really.

It honestly depends on when your girl was manufactured/which model she is. DDS Marisa, DDS Reimu, DDS Akira 1st version, DD Moe 2nd version, some Saber Extras, and some Saber Alter 2nd versions had early versions of the DDS/DDIII frames that were prone to cracking. If you have or buy one of those girls, then you'll definitely want the reinforcements.

 

Girls made after those five had a more current, clever design of the frame that only cracks rarely, but if you think you'll be handling your girl(s) a lot or have them holding heavy props, you may want to consider the reinforcements just in case.

 

Girls made earlier were done with the DDII frame, which had a completely different design. This frame did not have the cracking issue, and the reinforcements won't fit anything on the DDII frame.