Here is a comparison between the 2 Kits:
Horizon:
1/9 Scale or there about
All Vinyl Kit.
Needs a bit of work & customisation to make it look good.
Especially on the rear parts of the legs(solid but should be open), although minimal surface detail.
Argonauts:
1/12 Scale
Vinyl, Resin & White metal parts.
White metal parts are cannons(got 5 need 3) & and large screws for the rear part of the legs.
Resin: whole rear part section of the legs to get that section looking acurate.
Vinyl: all the rest.
Apart from the rear part of the legs the parts splitup is identical.
The Argonauts kit has more surface detail (wiring, etc), attaching the resin section to the lower legs will be fun as there is not much of a glue-joint.
center part where the hip-joints are sitatued is lacking the markings for where to open to fit the legs, will cut diameter disc and use those for guidance.
Advise:
Fill lower legs with resin and than pin the rear and lower sections together.
This will also give the kit weight and stability.
Overall I prefer the Argonauts Vinyl, a few pinholes but a pleasure to work with.