Once you get to the rank 2 PI-Tacs, every one of your team members (7 on the network) gets +1 to attacks, +2 to perception, +1 to stealth, automatic dosers of whatever drug you can imagine, a bonus of 2 (or 3, depending on interpretation) to the Firewall and Data Processing of the host device, and the ability to shift around Initiative Points. That's pretty damn powerful. The price is steep, but remember that you only have to buy it once and you aren't buying it based on the device rating. So a team of 7 people in 4th edition had to buy 7 copies of the software, and it had to be at level 4 (12,000¥ per copy). That's 84,000¥ by itself. But you also had to have each team member contribute 8 data channels to the feed. That part is where it got difficult and expensive. Buying all those sensors would be very difficult - that's no longer necessary.
The only hard part was sensor channels, and really wasn't that hard. Slap a simrig in your helmet and you've already got 3 channels, 4 if you're not human, since low-light and thermo count as separate channels. Then get glasses or goggles with smartlink, ultrasound, and either low-light, thermo, or both if you don't already have one of them from your simrig, and you're up to 7. You're only 1 sensor channel short of the maximum bonus and you've only got gear that a lot of characters have anyway. (Players love them some alternative vision modes).
As for the cost, it's only 12k per copy of the software. For the maximum bonus of +4, you only need 6 people, which comes out to 72,000 nuyen. Which is only about 445,500 nuyen cheaper than the cheapest 5th edition tacnet, which does nothing except give the entire team +1 to perception. Even if you have a massive team, including a small army of drones, and are achieving all of the sensor channels with expensive separate sensors, you'd be hard pressed to spend anywhere near 517k in 4th edition, let alone 824k or 1.2 million.
Also, you could totally just have a centralized Tac-Net, and have everyone slave their gear to the hacker (which everyone is probably doing anyway in 4th, especially if he's a technomancer.) Then you're only paying 12k for one copy. And if you are a technomancer, you could even thread the complex form for nothing more than a bit of fading.
As for what it actually does, +1 to attacks (4th edition gave +4), +2 to perception (Again, +4), +1 to stealth (+4!), Automatic dosers of drugs (not explicitly allowed in 4th, but totally doable if one of your sensor channels is a biomonitor), Firewall/Data proccessing boost (Not in 4th), ability to shift initiative points (Also not in 4th)
So everything the 5th edition version does, 4th did better at a higher bonus for a cheaper price. The only exceptions are the Firewall/Data Processing boost, and the ability to hand out initiative. Those are interesting, but certainly not unbalancing, and absolutely not worth the six digit asking price.
Tac-Nets in 4th were broken and needed to be nerfed, but 5th just made them too expensive and too restricted to be all that useful. It might as well have been included in a GM only section of the book, because players will never get to use one.
