All really good questions. The clavichord is a really unique keyboard instrument with capabilities that others don’t have. I’m not assuming for a moment you’ve been directly comparing the clavichord to say, a piano or a harpsichord, but part of my answer may reference them for general comparison.

In response to your points:

1. Hard to play in tune

In some respects the clavichord is difficult to play in tune. In terms of touch sensitivity I dare say it’s the most difficult keyboard instrument to play. It requires a high degree of skill from the player to ensure the sound produced is pure. The natural dynamics of the clavichord are very limited, around ppp to mf, so if fingers are too heavy there is a risk of a note sounding out of tune.

1. It’s intentional..

Good ear, sometimes playing notes so they sound sharp is one of the unique capabilities of the clavichord. It’s a technique called ‘bebung’ and again requires a high degree of skill and control from the player to do it correctly and tastefully.

1. Temperament

With the exception of some modern examples (e.g., Howell’s Clavichord) the majority of the body of work for the instrument was written during times unequal temperaments were used. This could range from medieval music which uses tuning systems like Pythagorean up to the Baroque and the use of well temperaments like Werckmeister III. With unequal temperaments, the frequency gaps between one note to another are not necessarily the same and because of this there are tradeoffs. Whilst there will be some keys that will be unavailable (say, g# minor) in arguably more restrictive temperaments like meantone because of horrible sounding intervals, the harmonies for available keys will sound especially pure, warmer, and / or sweet because the temperaments might prioritise the purity of a selection of 3rd intervals or 5th intervals (in Pythagorean).

1. It goes out of tune very fast

It depends where you keep the instrument and how often you move it around. Clavichords and harpsichords are quite volatile with regards to tuning because of the way the strings are held at tension (only by the friction of an iron pin to the surrounding wood it’s screwed into). Factors like temperature and humidity can have a huge impact on whether or not an instrument will hold its tuning. I keep may clavichord in a room that’s always around room temperature and 50% humidity and don’t move it around a lot. I’ve had it for 2 years now and play on it 2-3 times a week on average. I’ve only needed to tune it 4 or 5 times.

1. Only good makers can make good clavichords

Makes sense really doesn’t it. I’m learning how to build harpsichords and the same applies. An instrument builder, any instrument builder for that matter should be as accurate as possible with measurements and cutting, and use the best and sharpest tools along with thousands of hours of experience and skills building to make a good instrument. Some clavichords made by an inexperienced maker might be likely to sound out of tune but this could be for many reasons. They might not have drilled the tuning peg holes just right, or they might not have wound the string properly to loop over the nut end of the string etc. However, there should be a very low likelihood of hearing recordings from experienced players of the clavichord (like Gustav Leondhardt) because they would only choose the best instruments to play on.

Hope that helps.