I've been considering this piece of wargear recently, and thought I would see if anyone else had thought of any other uses for it.
Overview: The Positional Relay allows a model that has it, that is already on board to forego all potential reserve roles for uncoming units and instead make a single role for one unit that comes in on a 2+. It is Special Issue and Support System. This means that only Shas'O, Shas'el and Shas'vre in Crisis or Broadside battle armor. Unfortunately this means that stealths may not have it of course.
BASICS
The most obvious use for the Positional Relay (Hereinafter "PR") is to assist deepstrikers in coming down early on hard to reach, soft targets. Baslisks and other weak indirect weapons. Monat suits and gun drone squads come to mind. In conjunciton with the Pathfinder Beacon on the Devilfish, this means that you can deepstrike dangerously and have a good chance of landing effectively. In basic armies few lists put massive amounts into deepstrike and therefore most likely you will be forcing a single unit to come down on a 2+. A monat suit with your pick from the smorgesboard of options should be enough to do the task. In most situations using deepstrike like this is a sure way to lose the unit, due to assault, short ranged fire fight. But the threat of indirect against our suits is simply to much to be ignored.
LIMITATIONS
One of the initial limitations of the PR is in missions that have Escalation. In situations like this jet-pack wearing crisis suits will be forced off board and therefore the use of the PR cannot even begin until round 3 perhaps, and even then you may be hoping for more units to come on board then simply 1. At that point, one unit may not be good enough. This problem can partially be remedied by placing the PR on the broadside Shas'vre who is treated as Infantry however. This will of corse prevent him from having a Advanced Stabilization System, but that is a choice we have to make. In general Escalation is going to cause problems for this piece of wargear no matter what, as it's primary power: that of first strike deepstrike, is effectively negated.
LIMITATIONS AS ADVANTAGE
In brainstorming here and on the Advanced Tau Tacitca webside one of the single most threatening lists to the Tau is the All Drop Pod marine army. The primary tactical issue is that our untis are deployed on the board while our opponents can pick and choose where to fight when they come on off of reserves. The new Grand Tournament rules allow for 1/2 of the missions however to use Escalation. Wow the following comments will not help you in games where this rule will not be used, it may be of some use on games where you feel there is a decent chance of Escalation.
I would venture to say that most Tau players at this time in the metagame are running whole or at least 70% mech lists. Some may include a few static elements, but by and large transports and jet-infatry are currently in high popularity. Therefore in Escalation missions the majority, or totality, of our lists will begin off board, just as our most feared opponents, the Drop Pods will. Below find an example of it's use in an Escalation mission where Drop Podders have forced the Mostly Mech Tau list go to first.
Let us assume that you took a Single Shas'vre broadside with a PR. And it was one of the only, or few units on the board. In missions where Drop Pod armies play other all deepstrike or reserve armies they are forced to run a risk. That is, can they force their opponents onto the board before they can drop. If the drop pods are forced to drop first, before there is a large army, or in some situations any army at all, the advantage has gone to the list that comes down, or on board, second. This is where the PR comes into effect. Let us assume that the Tau lost the roll to see who goes first and the Drop Pod army forced the Tau to go first, thus negating one turn of fire, and also forcing us to begin rolling for reserves on turn 2, before our opponents. However, turn 2 roles around and we use our PR to force a single unit of gun drones(or single crisis, i.e. cheapest unit) on board, but leaving the fast majority of our force off board. It is now the Drop Podders turn 2. 1/2 of their army comes down and effectively has 200 points or less, perhaps 300 to shoot at. To attack it correctly they deploy the majority of their army against your broadside (that is behind cover at the edge of the board). Most likely they will destroy what you have on the board.
At this point, while you have lost a portion of your points, you have forced your opponent to show his hand and deploy a non-mobile force to the board. They all will most likely have two special weapons and bolters. This means their real danger is in 12 inches. Anything outside of that and they are not that impressive. We however have a large force to offset this that has come on in mass and is effective at range and can use the terrain to our advantage.
I am not sudgesting that this makes it an easy victory, especially in light of the fact they have an additional 50% of their army still off board. However it is a possible way to take some of the initive away from the Drop Podders and use their static nature to our advantage.