QBU-191's Skill is a whole lot of words and may bait players into making a cross formation Echelon. Don't. If you absolutely must use her, put her on pos4 next to the other RF. 

Before gaining Coins, QBU-191's performance is around half of that of WA2000's (who is the standard RF self-buffer). When gaining Coins, she gains 10% Critical Damage for 10 seconds, which can stack up to 20 times if enemies die swiftly enough. Additionally, for each additional battle, she will start with 5 more Coins. For example, in her 4th battle she will have already won 3 battle, and will thus start with 15 Coins, gaining 50% Critical Damage for 10 seconds at the start of battle. Additional Coins earned in this 4th battle will still only grant her 10% Critical Damage for 10 seconds. 

Her Synergy Effect triggers for each ally on her tiles, granting a random ally and herself a buff equal to her tiles (10% DMG, 10% RoF). If she sits on pos4 next to another RF and 2 HGs on her tiles, she will trigger this effect 3 times on herself and 3 individual times on random allies on said tiles. As it is RNG whether she will buff the other RF, performance can swing wildly from battle to battle. 

With all this in mind, from the 5th battle onwards she will start having somewhat equal performance with WA2000's baseline performance and the overall effectiveness of the Echelon is purely RNG as she needs to buff the other RF instead of HGs. Just use a normal self-buffing RF instead.