Yeah straight flush doesn't work all the time, neither Zing Zhen Hu. Trap jammer works fine for me, not sure if i need 2 but it's working fine with only 1.
Yes trap jammer is better than straight flush.
Trap jammer is a counter trap card, so you can counter it just with another counter trap card. And widespread ruin is just a normal trap card. Your final blow would be succesful .
Trap Jammer is the best choice if you have game with 1 attack (i.e. Union Attack, Gift of the Martyr), if you need multiple attacks, I would go with deckout and/or burn since having a consistent win would be harder to achieve.