Enphase has no single point of failure whereas the Solaredge system will completely stop if the inverter fails. So with Enphase you lose 1/16th of your 4kW system compared to all of it with Solaredge inverter failure.
Enphase outperforms Solareddge according to the ONLY independent test results available from PV evolution labs at :- dated Sept 2013 so very current.
http://www.metgen.co.uk/assets/download/index/assets/122/
There are three U tube videos available here about why Enphase is better
Enphase Inverters | Solar PV & Renewable Energy Trade Supplier | Metgen, UK
There is side by side testing regarding Enphase v SMA but it is a little dated and I need to find the link for it.
Solaredge seem to shout the loudest about being the best and keep on about Enphase capacitors failing despite the fact they and SMA use the exactly the same capacitors. We have over 100 Enphase systems and have had one unit fail as a squirrel decided to eat the cable which is hardly the manufacturers fault.
There is some evidence that systems over 14 modules are less efficient with Solaredge.
We have used all three systems but now only fit Enphase and SMA as both of these have superb customer support whereas Solaredge back up is patchy at best.
The Solaredge optimiser unit is about £30 on eBay and the Enphase micro over £90
which is also a guide. The Solaredge optimiser clearly marked as made in China on unit whereas the Enphase is USA or German.
i have an SMA inverter on my own roof and when it fails I will be upgrading my system to Enphase for the warranty and better performance.