That was an iffy guide then, medbay lvl 2 is always secondary at best. 2nd level teleport is nice because you can more quickly send a second wave of boarders in or retreat your crew in time to avoid asphyxiating on an autoship. But still, Mantis A has enough problems even that might be a waste of scrap.
Mantis A is one of those ships where the RNG can ruin your game if it wants to. Be prepared to run if you fight ships with no 02, and avoid abandoned/rebel sectors like the plague. On top of that you have no sensors, so be cautious around any ship which might have dangerous crew or an anti-personal drone. If you're OK with cheese strategies if you run your boarders around the enemy ship forever the enemy will only rarely be able to get hits in, which can save your boarders. Always go to mantis sectors. They'll teleport over, you'll kill or maim the boarders, then you can teleport over to their ship and finish them off.
Your bomb can be used for two variants of the 1-2 punch. One is to bomb their medbay/clonebay and then teleport two mantis on top of it, forcing the AI to fight you without heals. The second is to bomb their shields and then kill them with lasers. Unfortunately your weapons are crap, so you'll need another laser or beam weapon to make this strategy practical. Don't go for ion unless you get something more deadly than the basic laser.
Mind control SHOULD be great for this ship, but you don't have sensors so don't bother until you get something that enables MC. Hacking is nice but you don't have many drone parts so meh. Clone bay is arguably better than medbay but not to the tune of 50 scrap. I'd say build wise you should sell your pheromones and then go with the flow. This ship doesn't lend itself to any particularly great builds, so just hope you get a nice random drop and then transition into a build you know works. If you get a lot of crew go for teleporter lvl 2 or clone bay, and then spam boarders all day long. If you get a nice gun go for a conventional build. If you get a slug crewman go for MC. But yes, this is a luck based ship, as is the achievement for killing the crews of enemy ships (because you have to encounter crews to kill them).