Last month The Great Devourer finally became available over here, and we have been testing it out.
Although the cards looked very OP at first, we noticed that they did not pack the punch we expected.
Even with promotions you still struggle in the command struggle.
Since the Toxic Venomthrope needs to infest first to gain the extra bonus compared to the Void Pirate, the Rogue Traider and the Eldar Survivalist you tend to lag behind.
In addition, having no unique units make you very vulnerable to Exterminatus, Doom and Archon's Terror (and then there is AoE damage to deal with).
Having no option to counter any effects (like Routing or event cards) makes them rather vulnerable.
It is no surprise that we did not have any Tyranid Decks in the Dutch Nationals, which was dominated by Dark Eldar and Eldar decks.
What is your experience so far?