Purchasing upvc windows help

Hello this is my first post, I will get straight to it. I have built a new house in Co. Mayo and am at the stage of needing to get windows, I priced TJ GRADYS and a local supplier for about 21 upvc windows and two doors and got a price of 9000 euro off both, I asked about gaurantee and was told only six months on the glass as if there was any problem it would happen before then. I then asked were they argon filled and was told no because the use pilkington k glass and they said they had customers complaining thay were too warm, they said they had a U value of 1.88.
I was also told I could not have my french doors opening inwards as it would not seal properly. I was not happy with this so I contacted senator windows who told me I could have my french doors opening anyway as they had superior locking systems and better seals called a qulon system, thay had argon gas in the cavity and had a U value of 1.3 which raised to 1.4 when they were fitted to the window frames, and everthing came with a 10 year garantee.
This was all I wanted but the price was a hefty 14000 euro.
I then found a company in cork called hi-tec windows, they sell windows online and seem to offer everything senator offers for 6800 euro but I would have to fit them myself.
I am tempted to go for hi-tec windows but as they have no showrooms I am a bit unsure, does anybody know anything about this company, thay are based in cork and get the window frames made in clare I think.
I hope someone can offer advice.

Stay away from the first two companys, they obviously don't know what's up to date. Your windows will hopefully last a long time, so go for the best. A guarantee covers two years, that is EU law.
Senator do good windows but aren't cheap as you've found out.
I bought some from HELE, a company now in Midleton. Not to be recommended.
It depends on the size and weight of your windows, maybe you can install them yourself.
Or try any carpenter shop if they would do the job for you. And try to get insulated frames as well to avoid condensation occuring on them.