the gem prices seem way too high for any amount of gameplay. An average of 250 red gems for a x1.75 upgrade? that's more than 10 days of waiting with default gem speeds, and with +1% for each achievement it really doesn't speed up.
there's some cheaper ones at around 120, but that's still 5 whole days with no active way to speed up or strategize around it for an "alright" upgrade