Even a small hood will block the built-in flash. So, it's a good idea to use a coiled Canon TTL extension cord with the EF-X20. Works okay here, but I rarely use it as it is a pain in the rear to hold the X100T with one hand and the flash in the other.
If it is about ad-hoc on camera flash for snapshots, the Nissin i40 or the Meike 320 are both better options, the Nissin being very expensive unfortunately. If it's a planned setup any speedlight that has manual controls works great. I don't mind going back and forth for adjustments as it slows me down and makes me more considerate.