Xen's weapon was an incredible technological innovation; it blinded the Geth. I'd bet it could be adapted for use against Reaper husks.
It was a giant flashbang that made the Geth ships and ground units unable to sense where the Quarian ships were. There is absolutely nothing immoral about that; it's no worse than the Normandy's and the Salarians' stealth systems.
We have been told it doesn't work on the Reapers. It's probably a Reaper/collector gift anyway, for services rendered or salvage.
In Mass Effect: Ascention (Which is between the 2 year span between ME1 and 2) Kyhle Sanders provides the Quarian admiralty with intel and information on the Reapers and Sovereign after the attack on the Citadel and warns them so that they can prepare for the Reapers.
The Quarians had been discussing Searchign for a new homeworld and sending out explorer fleets but interest was cool at best, (I guess Koris was the onlyone interested, possibly Raan) But once they learn about the Reapers they are suddenly interested and decides to send out explorers to find either a suitable new world, or Reaperships to help influence a removal of the Geth from Rannnoch.
2 years (ME2) later we meet tali as she and a team who's very worried about anyone getting to Veetor before they do. All security mechs on the collony had been disabled before the Collector attack on Freedoms progress. But after the Collectors had left and you land in a Cerberus shuttle they were reprogrammed to attack anything that moves and activated.
The only living person in the whole colony left is a Quarian who choose a very unusual location for a pilgrimage, and Tali and her team who seemed to think Tali didn't know what was best in the situation, was sent there by her Father Admiral Rael Zorah to pickup Veetor. The Quarians arrived from the other side of the galaxy, several relays away to respond and save one Quarian before anyone else had time to respond.
Even before Cerberus who had been monitoring and tracking these events to try and expect where the next attack would happen and responde before everyone else.
You then find Veetor who instead of activating the mechs from the security room during the Collector attack just sat there collecting security records and data. Then when other people (Cerberus in a human shuttle arrives unexpectedly) activates the mechs and disables all safeties instructing them to shoot anything that moves.
TIM tells us very little is known about the Collectors but they are known for trading technology for services rendered, usualy in the form of testsubjects.
◾According to Mass Effect: Incursion, Freedom's Progress had a population of 912,810 in 2183
It also wasn't the first colony taken.
Weeks or months later we encounter Tali on Halestrom where we learn that her father has been sending her on covert missions to collect Geth parts and technology for his research. But this was her last mission and she decides she can join up with Shepard for a while.
Later still, Tali is recalled to the Fleet due to problems arrising from Admiral Raels experimentation with his new anti-Geth technology where he had ordered the removal of all firewalls and by passing of normal securityarrangements because he was so sure of what he had that he prefered expedience over a safer more cautious approach. This resulted in his death and that of his crew because his Geth testsubjects managed to turn the tables on them and surprise them.
His last dying words for Tali was for her to get the research to Xen and Han on the admiralty who were his allies in all of this. They in turn were worried about what might come out of this incident and potential political implications.
So, we got;
Admiralty order to find Reapers and aquire reaper technology or influence to get rid of the Geth, or a planet to live on.
Strange Quarian activity and unlikely turns of events on Freedom's progress.
Leading to a new superweapon that the Quarians hadn't been able to produce/develop for the past 300 years, but all of a sudden it's deviced in no time at all with minimal resources covertly allocated. The Quarians on the research ship sounds like idiots with no idea what they were doing, which likely helped them get themselves killed.