I have no experience of any system and would welcome advise from anyone who
has used either of these or other automatic watering systems.

I've used variations on Raindrip systems for about 20 years now. It consists
of small diameter tubing (0.25") that can be connected to a hose bibb,
and from that can be connected drippers of various types, with drip
amounts varying from about 0.25 gallons (approx 1 liter) to 2.5 gallons
per hour. Choose the dripper based on the size of the pot and the
water needs of the plant. Connect the whole system to a "water timer"
that has a solenoid that opens to allow water into the system for a
preset interval, and you've got a fairly decent automatic watering
system. The big issues are quality of the water (sand or very hard
water can block the drippers), reliability of the water timer, and
initial set up, which for 20 pots, would probably take me about an
hour. I prefer the drippers that can be taken apart for cleaning --
Raindrip's design is called a "flag dripper".

Because the water is going directly onto the soil, and not onto the plant,
you tend to have fewer problems with fungal diseases, and there's little
wastage of water, as you might have with a sprayer system.

Here's a website with more information:
http://www.raindrip.com/

A suitable water timer:
http://www.dripdepot.com/1006.html?id=tUYEBaiL

I'm guessing you're not in the US, so you may have to shop around to find
something similar; perhaps you can find something similar from a maker of
greenhouse drip watering systems.

Kay