From what I can see, the spiral box has no overlap with the 300pt box (which I have), and all the models are usable in Tohaa, but are they models worth getting?
Some work better than others: - Clipsos: awesome profile. I don't know how many times you'll need two at the same time, but they are cheap and work very well on many missions, so it complements nicely the 300 points box. - Kiuutan Imposter: vanilla Tohaa only has access to one Kiuutan profile, but thanks yo Jaan Staar (Kiuutan character) we actually have access to two different profiles. Once you have deployed it a couple of times, your opponents will be afraid of it. - Draal Saboteurs: expensive profiles, but a great toolkit providing both firepower and a specialist that deploys near the middle table. You can also use them to proxy the OOP Sukeul Commandos. - Kiel-san: it's a pity that you cannot link it in vanila Tohaa, but it is a good profile and you might get fun results depending on Metachemistry. - Krigel Agent: unlimited Pheroware and the Phero-Booster (surprising weapon with good range, uses Will instead of CD, doesn't allow cover for the target and applies Targeted) makes it an unusual trooper. Good addition. - Taagma Schemers: Nice for deception, cheap enought that you can replace a basic Kamael in a Triad and deceive you oponent making it believe you are bringing something more powerfull. - Reex Escorts: use them to proxy the Kawaii Sentinels. So, to summarise it, the answer to your question is yes, it is worth.
Short Answer: Yes. Long Answer: what @Abrilete said Slightly Longer Answer: It also sets you up quite nicely should you feel like playing Spiral Corps instead of Tohaa; you basically only need to add the Taagma Sniper Blister and you're good to go. Maybe a box of Helots, though they're less popular in N4 than they were in N3.
If I may add some future recommendations... Chaksa, great both in vanilla Tohaa and Spiral Corps. The Chaksa Auxiliars Box comes with 4 Chaksa models, two of them armed with Flamethrowers. They are not only good on their own, but they are also great proxies for the Rasail Boarding Team (your Kosuil or Draal miniatures + Chaksa = your own Boarding Team), the Servants for the Kumotail and, even in a pinch, the Chaksa Longarms. Just make sure your oponent understand what your proxies represent.
Side note: if you can get your hand on a Gorgos, you can proxy that as an Anaconda in Spiral. OR if you can't find a Gorgos, get an Anaconda and proxy it as a Gorgos. Same size and very similar fire power. If you want, exchange the Anaconda's head for a Fraacta head to make it look more Tohaa.
Worth an extra mention that the Taagma Schemer also brings Counter Intelligence, which if you are going first is very useful.
