Is this feed, suitable for ham purposes (transmission power: max 100W) ?

It's certainly useable. For a short run, the losses would probably be
acceptable (20 gauge conductors aren't great but aren't terrible)
especially when it's dry and in new condition. In wet weather it's
going to be lossier than ladder line or open-wire line, although at HF
frequencies this additional loss may not be significant.

If you try to use it with an antenna which is badly mismatched for the
frequency, the high SWR on the line might lead to significant heating
of the line at 100 watts - this will depend on the impedances
involved. I have no idea whether the foam dielectric in the cable
would be adversely affected by the heat buildup at the high-current
spots on the line, or might arc over at the high-voltage spots.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!