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. :D
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!! :D