I don't get consistent shots, whats the cause? Should I get a new grinder? [Gaggia Classic E24, Kingrinder K2]

I use a 30 euro coffee scale, and a Kingrinder K2.

Today I made two espressos after each other, the first one took 36 sec, for a 1:2.5 dose, the second took 24 sec, from the same amount of coffee beans.

I'm wondering what could cause this, the scale or the grinder?

I really like grinding by hand, so I thought I will get a better grinder, do you think that would help?

Which would be a bigger improvement, these are my options:

1zpresso J-Ultra

OE Lido OG

Kinu M47 simplicity or classic (what's the difference?)

Or if I have to give up hand grinding for consistency a used grind by time Mazzer Major.

Or should I just get a Bookoo scale first?