I received the two 18 element yagis for 1296 Mhz and they appear to be strongly made. We will see whether they are any better than the previous antenna. I have borrowed a splitter for them and will use that for the Summer field day in mid January, unless I can make my own before then.
I found a website offering data on stacking distances for yagis. For a boom length of 1.5m on this frequency the stacking distance recommended is 2.4 wavelengths, which works out at 55cm (23cm wavelength). The feedlines on the yagis are about 25 cm long but that’s not long enough to reach the power divider, so additional connectors and cable will be needed, eating into the stacking gain.
Next step for 23cm is to configure the power amplifier so it can be operated remotely from the tent. I read some comments on the UK microwave reflector about power levels from IC910H not being up to the 10w level expected. Time to get out the power meter and check mine out.