If you decide to go the uke bass route I found that the Road Toad Pahoehoe (now owned by Kala) rubber strings have a really big 'blooming' upright bass sound over any steel string (rounds, flats or tapes). There is also less electrical buzzing interference noise with the piezo pickups. The only drag is the rubber strings themselves which, as someone pointed out earlier, can be sticky and a major PITA to install. But the ultra low tension makes them very easy to play. The Gold Tone uke bass second from left has rubber strings.
As of late, the increased proliferation of steel uke bass strings have allowed for magnetic pickups and more traditional electric bass tones in a small uke sized package. The right four basses all have magnetic pickups and steel rounds and tapes. The kala solidbody is very well made for its price.
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