After trying this 0.5 black Gel refill for the Ohto pen it is now my favorite.
Until I discovered Jetpens I had been using the Uni-ball 207 0.5 (micro)
cartridges (scavenged from 207 RT pen donors) in my Ohto pens. The G-305
produces a slightly darker black than the Uni 207's. Otherwise the performance
is similar and the sealed metal cartridge is a plus compared to the plastic
207's. The only reason I would not use these would be cost as you can get a two
pack of the Uni 207 Rt's for about $3 vs $5 each for the Ohto Gels.