There are two different (and non-exclusive) ways of looking at Cyberdex Sandbox.
The first is as a piece of tech hedging against virus decks. It gives you a free purge on score and repays the credit cost of the score (but not the clicks!), and it makes future purges forced by threats such as Medium less of an economic setback by compensating you with 4. Compared to Cyberdex Virus Suite, the existing neutral standard for virus hate, you get a more reliable and repeatable upgraded purge ability, and your tech card takes up an agenda slot, which is generally better to make sure you get enough space for plenty of ICE, economy, and other utility cards. While Virus Suite charges you 3 and a for a manual purge, it is also an ambush which can shut off Archives from Datasucker or Aumakua counter farming. The fact that you can purge with a pre-installed CVS also makes it a shoe-in against Clot if that card is likely to hamper your fast advance plans.
The second is as an economy agenda that immediately somewhat compensates you for scoring it, and then offers a slight improvement over spending on basic "take a credit" actions. This isn't fantastic, but I think it does compare favourably to the now-rotated Gila Hands Arcology; the immediate buy-back of 4 makes scoring much less painful, although it probably takes two or three more manual purges to actually be economical. Not great though when Corporate Sales Team pays out 10 without demanding any additional clicks, and it pays that out relatively quickly too. If you just want cash, Corporate Sales Team is virtually always better, and it is even the same advancement requirement to points ratio.
So, if you're going to play Cyberdex Sandbox, you have to want the purge and not just the credits. If you're playing a lot of fast advance, Cyberdex Virus Suite is still going to be your first choice of virus hate, but Cyberdex Sandbox can carry tempo and glacier decks further by offering repeated economical purges. Of course, if Freedom Khumalo: Crypto-Anarchist somehow becomes the runner meta you could play both, and if you don't need virus hate at all, then you don't need either.
One final note is that Cyberdex Sandbox, over all other virus hate, actually self-synergises and rewards you for purging through other card effects, such as Macrophage and Reverse Infection. You score a second Sandox and now you get 8 and you can spend for 8 again whenever you want! Maybe you do want to play both Cyberdex Sandbox and CVS after all! While this sounds like a huge deal and a powerful way of playing this card, I actually think this is at best a fun gimmick, and at worst an outright trap. It is not easy for most corp decks to stomach multiple 2/4 agendas, and there are plenty of others you can score twice (like Nisei MK II or over-advanced Project Atlas) that can straight up win the game and don't demand going all-in on virus hate that will be largely dead in some matchups or until you score your vulnerable 2/4. All Nisei MK II needs to support it is some good taxing ice and a functional economy, and unlike Reverse Infection, you were probably playing those anyway.