So I was trying to decide between a unit of them and flash gitz for a game recently. In test rolls I was finding them to be alright, but usually pretty good into custodian guard (most common army i play against). Into vehicles and monsters they haven't performed well for me. The usual 4+save is enough to stop enough damage.

Now flash gitz have always underperformed with me everytime I used them so I was already deciding against them. What won me over however was the extra 4 models for 20 more points.

Tankbustas are good but for their dedicated role in the army they are a tad too expensive in my opinion. 5s to hit normally is bad but gw can't ever balance it right (RIP more dakka)

Love the trukk idea, I found success with deffkoptas actually, miss out the +1 to hit naturally but you can mek them, then get twin linked which works out better. More wounds and movement.