Pondering further....I'm not sure you even need to restrict their activities to holding identified choke points.
Classic tactics against Tau are of course to try to close the range. Whilst one can beat them in a firefight, best results are gained from beating them up in hand to hand, and transports, drop pods and deep strike are fairly decent ways to close the range whilst mitigating incoming firepower.
But these guys? Very little wants to wind up within their 5" range - and given they're assault weapons, that could be extended to a fairly respectable 11" 'nope' zone. Their mere presence will somewhat dissuade deep striking close to Tau lines, which can help to make the whole exercise pointless - as thanks to Jet Packs up the wazoo, Tau are an absolute sod to try and outflank and envelop.
Downside is a major vulnerability inherent to all Firewarriors. T3 and Sv4+ isn't exactly difficult to overcome. Whilst their potential Invulnerable save is nice (and helpful against Heavy Bolters and their equivalent), it may not come into play that often, as you certainly don't really need AP4 to deal with them - your bog standard Infanty dakka can deal with them fairly swiftly - and those are guns often wanting a decent target against Tau (Ghostkeel, Broadside, Stormsurge and Riptide all scoff at your weedy small arms - even Crisis Suits can afford to treat them will mild disdain)...
So to me, this means whilst they're likely to be a priority target for your opponent, they won't necessarily be taking the heat off other units in return. That's a tactically odd place to be, so as an owning player you'll need to be thoughtful in your deploy and subsequent support of them if you want to keep them active beyond the first couple of turns.
Hmmmm.