>>6439602>>6439685 summed it up nicely in one word! To go into a bit more detail, MSIA height was around 3.75 inches (I think? I'm not sure where my MSIA are to compare) while RDs average around 5.5 inches. RDs are also generally made with a much more rigid, yet still very sturdy plastic, while MSIAs were made with a softer, rubbery PVC. This allows RDs much sharper sculpts and molded details than were possible for the MSIA line. Additionally, RDs are designed with range of motion in mind (especially nowadays), so their articulation is generally excellent. The leap in detail and articulation from MSIA to RD really can't be overstated enough.MSIA still has a couple strong points, though. First, they're nigh indestructible thank to their soft PVC construction. RDs are designed to be messed around with and are not fragile by any means, but they are intended for adults so they can have parts that could break if you're not careful (antenna and things like that). Second, there's the price. Even now, you can pick up MSIA for fairly cheap second hand, while RDs are gonna run you $40-50 or more a pop. Lastly, MSIA has a much wider variety of mobile suits. RD is catching up and has stuff MSIA never had (ie Gundam Sentinel), but it still has a lot of gaps in its mobile suit representation coverage (for example there's nothing from 0083, and very very sparse representation from 08th Team and 0080, but the ANIME line makes me optimistic that these gaps will be filled), though this is offset by the fact that RD covers a much large variety of series.
If you have a mobile suit or mecha design you particularly love, and there's an RD of it, I heartily suggest giving the line a shot! While pricey, RDs strike an awesome balance of detail and playability that's unlike anything else. As someone who built gunpla and collected older Gundam toylines for years, the first RD I bought really blew me away. Seven years later and now I've got waaaay too many RDs, haha.
