The toy's name is just "Megatron" but the sub-line is indeed "Transformers Choro Q Robo."
Choro Q is a line of miniature "cute" cars with pull back motors manufactured by Takara (first released in 1978), so it's a like a crossover.

Although it's not the first time - Microman also crossed over with Choro Q in the early 1980s and indeed G1
Bumblebee,
Cliffjumper and
Bumblejumper are all actually based on Choro Q toy cars - that's why their alt modes are super deformed (most noticeably Cliffjumper's if you compare with a
real Porsche 944). Choro Q toys were imported into some Western markets as "Penny Racers." I used to have the
Choro Q game for Playstation - my favourite car was the dump truck and tank which I would modify with the best body kits and engines to make them super fast.
The toy you got is the black variant of Megatron (Takara had an obsession with black variants in the earlier part of the 00s). There's also a
regular coloured version as well as
Convoy and
Rodimus Convoy. There are metallic variants for
Choro Q Convoy and
Rodimus Convoy.
I really love how Choro Q Megatron, despite being a Walther P38 pistol, still has wheels and a pullback motor which allows him to roll around in gun mode like a regular Choro Q car!!
