The touchpad works well with multi-tap and can handle single/double/tripple tab. Feel free to map that to the middle mouse if needed.
The keyboard is actually quite good once you get used to it. I used to need a keyboard replacement every 12-18 months on my lenovo (yes, you read that correctly). The Dell one has now survived 12 months, so I'd say the build quality is quite good, perhaps even better than the lenovo one (might also be due to design - nothing gets stuck under the keys, which helps a lot).
Dell has even send me replacement parts in the past to repair stuff on my own.
edit: I realize after posting this it might not be relevant since you may be discussing the trackpad as used with Ubuntu.
As of 1 month ago, when I bought and then returned an XPS 15 due to the trackpad, there was no option for middle clicking and no option for navigating forward/back.
There are also horrific sensitivity issues with the trackpad that is extremely well documented in user complaints online - the cursor doesn't start moving until your finger moves about a millimeter on the trackpad, resulting in it "jumping" when you are moving very small distances with high cursor speed.
These are all software issues - I installed Synaptics and it fixed these problems, but introduced others. I spent over 20 hours testing and researching and messing with the registry to have a trackpad that works the same as most any other laptop with Windows 7 or Windows 8.1. I obviously didn't succeed, which is why I returned it.
To clarify, this is really a Windows 10 issue, and to some extent an Synaptics driver issue (even though it isn't officially supported by Dell).
Synaptics is terrible (at least from using them on ThinkPads for years). It loses settings, frequently. When using the trackpad, it uses several percent of CPU. That's idiotic.
For what it's worth, I had a bad time with the trackpad with a default 14.04 install. Switching to 14.10 fixed it, presumably due to the inclusion of newer drivers.
The keyboard is actually quite good once you get used to it. I used to need a keyboard replacement every 12-18 months on my lenovo (yes, you read that correctly). The Dell one has now survived 12 months, so I'd say the build quality is quite good, perhaps even better than the lenovo one (might also be due to design - nothing gets stuck under the keys, which helps a lot).
Dell has even send me replacement parts in the past to repair stuff on my own.
[EDIT] type.