Smartvent VS DVS vs SAYR

I can't see if you said where you live?

But in any case, just get one. It'll fix your problem.
In my opinion, Smartvent (Positive 2 system) is the most reasonable price for a system that can be expanded with options like the summer kit, or heat transfer.
Or they have a Smartvent Lite which will be cheaper, but can't be added on to.

The quote I had for the smartvent positive 2 system was actually the most expensive out of the lot I have had quoted. DVS and SAYR were both around 2900 for a 4 vent system. Got quoted 3100 for the smart vent. Have thought about purchasing the smart vent system and getting a local sparkie to put it in. But havn't sat down to see if that works out any cheaper

Condensation on windows is normal and can be solved by opening the windows in the morning until the condensation goes away.

I prefer not to have it in the first place, so just keep my house warm.

you were lucky we used to live in a rolled up newspaper in the middle of road, wake up every morning and lick road clean wit tongue, and then our dad with thrash us to sleep with his belt, and you tell the young ones that today and they wont beleive you. (Quote Monty Python, Hollywood Bowl)

Condensation is caused by the air condensation on the colder surface. If you had double glazing the condensation would still be there.

I would advise against having the system running at night as otherwise it will be pumping cold damp air into the house as the air outside tends to be cold and damp at night,

it depends on how cold the window gets.
single glazing gets cold easily so often gets condensation. double glazing requires much lower outdoor temps to ge the window cold enough, so a lot of double glazing will not get condensation.
but given cold enough weather and high enough indoor humidity, you can still get condensation.
however with weather that cold you tend to get cold but dry air, so a bit of minor ventilation easily keeps the house dry and avoids condensation.
its not just one thing, theres a few things going on.

ventilation systems should always be running, most will slow down to minimum speed simply to stop indoor air flowing back up in reverse. keep in mind at those really low air flows, your house leaks more air in and out anyway than what the ventilation system is pumping in. so its not really making the house any colder than it normally would be.

I installed a Smartvent Positive in a student flat today. The students are away on holiday, but when I got there most of the windows in the house had condensation on them even thought there hasn't been anyone in the house for a few days. While I was working there all day, there was still condensation on the windows, even though I had the door open and the manhole open as well. It probably got to about 7-8 deg in Dunedin today, and this house got very little sun, if any at all today.
I turned the system on around 4pm, and had it set on high for about half an hour while I adjusted it. After doing the settings, I could see on the display that the roof temperature was dropping after 5pm. It went from about 7deg in the roof at about 4pm, to less than 4deg around 5:30.
I had it on boost (high fan) again for 20min while I cleaned up and put my gear away. By the time I left, about half the windows in the house had almost no condensation on them. That's despite the roof temperature being more than 5 degrees colder than the inside house temperature. (there was no heating on all day).
So they work, even in cold weather with little sun on the house or roof. The system will shut off automatically overnight because of the cold roof temperature, but once it's above 5 deg in the roof tomorrow, the fan will start again.

You would be best to actually get a local sparkie (that sells Smartvent) to sell you the system and install it. I wouldn't be interested in installing one that someone had bought themselves. Apart from the warranty issues, there just isn't enough money in only doing the installation without selling the unit as well. And pretty much everyone has enough work without installing stuff that clients buy themselves.
If you call Simx, they will tell you the installers in your area.

hrv changed owership,we had it installed to rid crying windows,it is perfect.no moistere at all.we have a heat pump for warmth.