Nice, but was having Forth *onboard* sufficient selling point for otherwise generic hybrid?
I've heard about the Jupiter Ace before, and I'm certainly not criticising its brave (and interesting) decision to go with something different than the over-ubiquitous and bad-habit-forming BASIC- quite the opposite.
However, the fact that Forth was its unique selling point- to the extent that even in discussions today it seems to overshadow the spec of the hardware itself- seems somewhat unusual when you consider that implementations of Forth were- or could have been made- available for many computers that used BASIC. Granted, it might have been a pain- and a waste of RAM- to load it from tape, but surely it would have been possible to implement it as a cartridge (or a rampack-like ROM-based add-on for machines like the ZX81).
If we disregard the language for a second, the Jupiter Ace was somewhere between the already-established ZX81 and ZX Spectrum in terms of spec, and the market was already sagging under a ludicrous number of 8-bit home computers (my Dad's "Your Computer" magazines from around 1982-84 seemed to have reviews of between 1 and 3 new- and mutually incompatible- machines every month).
It might have been a decent machine for the money, but was there sufficient space in the market for it? And perhaps this is why it failed. Having Forth *onboard* (rather than as an add-on) might have been good, but perhaps- when people came to plonking down their cash- people realised that it was simply an aspect- and differentiator- of the machine, which was otherwise somewhere between the better-supported ZX81 and Spectrum.
I appreciate that Altwasser and Vickers (quite understandably) wanted to make money for themselves, rather than Sinclair, and that building a machine around Forth probably got more attention than selling a ROM-pack for the ZX81, but it was also a higher-risk choice.