The algorithm in this game dislikes me intentionally. I amount of my sworn swords successfully completing their journeys are low, even with a 85% chance. If I have a 85%-95% success rate, I lose 7/10 times. This is bull. Almost every time I lose high percentage success rate and the 60% rates are more like 50/50 chance.
Before using this upgrade, as of I think would be beneficial, you should have the following: rank at max level and all medals
(You should have $3,615)
1) Start by upgrading your ship twice
2) Buy level 4 weapon and level 4 loot
5) Kill 1st boss
6) Get $2,000 and buy lv.4 flag (Get the amount before 2nd boss)
7) Kill 2nd boss
8) Get $2,000 again (will be faster and you will get over the amount before final boss)
9) Upgrade your ship again
10) Get $1,000, buy lv.3 flag
11) You should be on the final boss
12) After killing final boss, you should have over $5,000, if not, get it then upgrade ship to max level
13) What I did was buy level 2 flag to get money, but you can do whatever from here. If you buy all level 5 upgrades, you will have 7/8 marks overall. If you go with my upgrades, you will get: weapon 7/8, fire rate 5/8, speed 3/8, loot 8/8, magnet 8/8 (technically 10/8). I found this very helpful because I had $29,000 (would've had more though). Hope this helps everyone out.