This is just a minor conflict, but both of these mods are very high quality and this is the only way in which they clash.

Preferred resolution

• Terrestria uses Biome Makeover's Saguaro texture, model, and icon. The needles stick off of the body a little, matching vanilla cacti. And the model never creates loops when you place several blocks together.
• Terrestria adds a composting recipe for the Saguaro to match vanilla cacti.
• Biome Makeover uses the Terrestria Saguaro sapling so that their cactus can be grown.
• Biome Makeover's cactus uses the terrestria texture to show that the cactus has been damaged.
• Users may choose to hide one or the other in REI to avoid duplicates showing even though both are identical.

The same issue: TerraformersMC/Terrestria#229

Obiously renaming one or the other is another easy solution =]

Oh, the Biome Makeover saguaro actually grows from individually placed cactus blocks rather than from a sapling. That might be a better behaviour for matching vanilla.

We're probably not going to do anything about this.
They don't conflict in any game breaking way that warrants any action on our end imo.

Also ours can be composted (or at least should be, open a separate issue if not)

Fair enough. It's easy enough for me to fix it myself. Keep up the good work. This mod is great =D