Why isn't he a good option? Seems to me like making your opponent reroll is a great survival trick.

Because killing your opponent first is a better survival trick.

It's a toss up of either r7 or m9g8 on Tarn, though most prefer m9 for the ability to modify friendly red dice.

On any other ship, it relies too much on accurate prediction to have any effect at all and even then is usually not really better than a focus would have been.

Acquiring a target lock usually requires spending your action. In this case you're usually better off taking a focus or an evade for your defence.
On paper the synergy with FCS can fool you into thinking it would work well on an E-Wing, but in reality it would only work for a high PS pilot, as you need to shoot before your opponent does (same problem R3 Astro suffers from), and on a high PS pilot, there are much better named droids.

As @hargleblarg said, the only real use is on Tarn Mison, though now you're probably better off taking M9-G8.

tl;dr the generic astros suck. R7 is good on Tarn, Targeting on Hobbie, an R2 on an X-Wing (purely as it's the cheapest to trigger IA). I really hope future generics are of much better quality.

5 minutes ago, hargleblarg said:

It's a toss up of either r7 or m9g8 on Tarn, though most prefer m9 for the ability to modify friendly red dice.

On any other ship, it relies too much on accurate prediction to have any effect at all and even then is usually not really better than a focus would have been.

M9 also works multiple times per round which R7 doesn't. Tarn can keep changing his lock to every ship that attacks him, potentially, and reroll a single red from each.

M9-G8 does not use the TL, R7 does. I learned that during a tournament as I've never used M9G8 before because I just assumed it would use the TL.
On the flip side, R7 lets you reroll all dice, M9G8 just one. But M9G8 is still better, even on Tarn, because you can use him on every attack while R7 is once per round.

So R7 is not even good on Tarn because you have a better option. And of course Tarn is not the top tier ship anyways

Just now, thespaceinvader said:

M9 also works multiple times per round which R7 doesn't. Tarn can keep changing his lock to every ship that attacks him, potentially, and reroll a single red from each.

Haha, I never even noticed the "once per round" text on r7. Was that really necessary, ffg?

Just now, GreenDragoon said:

M9-G8 does not use the TL, R7 does. I learned that during a tournament as I've never used M9G8 before because I just assumed it would use the TL.
On the flip side, R7 lets you reroll all dice, M9G8 just one. But M9G8 is still better, even on Tarn, because you can use him on every attack while R7 is once per round.

So R7 is not even good on Tarn because you have a better option. And of course Tarn is not the top tier ship anyways

I think Tarn can be pretty good. Just give him a single Plasma Torpedo, and Guidance Chips, and drive to get someone at range 2 or 3 in arc, then focus. Come on, attack me, I dares ya.

1 minute ago, thespaceinvader said:

I think Tarn can be pretty good. Just give him a single Plasma Torpedo, and Guidance Chips, and drive to get someone at range 2 or 3 in arc, then focus. Come on, attack me, I dares ya.

I run that Tarn, Hobbie the same but with TA, and a fat Jan Ors.

Bait with Tarn so he can get a focused 5 dice shot, then K-Turn behind with Hobbie so he can do the same.

4 minutes ago, hargleblarg said:

Haha, I never even noticed the "once per round" text on r7. Was that really necessary, ffg?

They are absolutely terrified of how broken everything would be if there were good generic astromechs available (to rebels).

2 minutes ago, thespaceinvader said:

I think Tarn can be pretty good. Just give him a single Plasma Torpedo, and Guidance Chips, and drive to get someone at range 2 or 3 in arc, then focus. Come on, attack me, I dares ya.

That makes him ok, sure. But Are those really the best spent 26 points? Better than a TLTstresshog? Or Biggs? Now you even have the Kashyyyk defender in the same point bracket, with 2 points for a crew to spare.

No. But it's funny.