A different method, requires a little practise, but quick & easy once you have it. This method keeps the seeds, but loses the harder green bit where the stalk was attached.
This is the quickest manual method I have ever seen & produces evenly sized chunks - it takes considerably longer to explain than to do. It requires a razor-sharp knife, otherwise you tend to just push the tomato out of your grip & lose control of it.
Place the tomato stalk side down, for initial stability*.
Make an even number of vertical cuts, parallel to each other - so you get 3, 5 or 7 equal-thickness slices, depending on tomato size & required chunk size. Don't let go, keep the tomato complete in your hand.
Now it gets trickier, because you have to constantly keep hold...
All horizontal cuts are only half way. All vertical cuts are right through to your board.
You no longer need to count how many cuts for the rest of the task.
Make several horizontal cuts at 90° to your first ones, parallel to your chopping board - but only half way through. It's more stable if you start at the bottom & work upwards. (Yes, you are cutting towards your own hand - be careful)
Slice again a couple of times vertically, at 90° to both existing cut directions, until you reach about halfway (all these 'halfways' become clear by the end) - & off come your first few chunks; slide to one side with your knife.
Rotate the remainder onto the flat face.
Make similar horizontal & vertical cuts; freeing your second set of pieces.
Rotate the remainder again, onto the face you just cut.
Depending on the tomato size, you may have room for one last horizontal cut, then make a last set of vertical cuts.
If you got the first counted cuts just right, your 'stalk' piece is separate & ready to discard.
* I've tried this both ways up, as it always feels as though being able to see the stalk when making the first cuts would be better - it isn't, you lose stability & are likely to lose control of the tomato half way through.