If I remember correctly you can also get a Tyrannocyte for them. The drawback to this is, of course, the Tyrant/Swarmlord can't take any Tyrant Guards with him due to them not fitting in the same pod. Also they can't charge on the turn they arrive and will not be able to provide you with a synapse bubble until turn 2 at the earliest.
Either way, a Foot Tyrant is basically going to need a lot of points investment to make him work, so either go the deathstar route or only use them in large games.
Personally I just run a Vanilla Tyrant with a retinue of 3 Tyrant Guards as a fire magnet. My real threats are my fexes and Trygons (hey, they might be nerfed but 6 S6 AP2 attacks on a monster with 6 wounds and deepstriking is nothing to to sneeze at). Generally having my Tyrantstar within charging distance on turn 2 along with one or more Trygons arriving will cause the opponent to start panicking at the multiple threats showing up. However it's expensive as hell.
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