I think the TNT is useless in multiplayer because it is very unlikly to roast someone unless they are trying to kill you. However, since the AI of enemies in SP aren't too intellengent the TNT can be effective against them. The freezer is useless in some ways such as killing. But when it comes to anoyying your opponents or sometimes getting away quickly enough it is quite a good... well utility because it shouldn't really be considered a weapon.
The freezer is also effective against enemies like above.

Conclusion: TNT should not be used as weapons but for certain other occasions.