Really, really weak. You should not use this in your deck,
(Unless you intend to be doing HQ lock, which is the criminal's specialty, or (maybe) in an anarch economy control deck).
Lets look at the numbers:
Easy Mark: At cost 0, gives you an unconditional burst economy profit of 3. It is rarely used, due to how good its counterpart is:
Hedge Fund: At cost 5, profit 4, Runners usually have this required amount or can comfortably click to it.
So, Lamprey needs to provide at least a profit of 4. Its install cost is 1, which means it needs to produce an economic advantage of 5. That means you need to run on HQ 5 times before breaking even with Hedge Fund. This is conditional economy, as you only gain those credit advantages when you run on HQ, and it distributes the gain over several turns, so its also drip economy, making acquiring them much more difficult and awkward. In addition, it uses up a memory slot in the meantime, restricting the use of other more useful programs, and is trashed when purged, which is likely to happen multiple times with anarch runners, so it may not even pay itself off. Even if its memory and install costs were 0, it would still be roughly at level to Easy Mark, which is rarely used.
However, it (might) be worth (considering) in anarch decks running Bhagat and Wanton Destruction, or in a control deck with Ixodidae.
In conclusion, throw it in the binder and forget about it.