If the alto is bigger than the treble, why does it have fewer tines?
The Treble kalimba, on the left, has 17 tines, while the larger Alto, right, has only 15 tines. The Alto tines are larger. The Alto tines have more space between them, and I find them to be easier to play - they require slightly less precision than the treble. At the same time, the treble tines are closer together, and a precise player can actually play faster on the Treble. People with large hands tend to prefer the Alto. Those with smaller hands tend to prefer the Treble.
The Alto kalimba's box is 8 x 5.5 x 1.5 inches, and the Treble's box is slightly smaller: 7 x 5 x 1.25 inches. The Treble's tines are 4mm wide, and the Alto's are 5mm wide, so you can fit 17 Treble tines into a space narrower than the Alto's 15 Tines. A typical Alto kalimba will weigh about 1 pound = 16 ounces (0.450 kg). A Treble kalimba will weigh about 12 ounces (0.335 kg). However, there is a lot of variability due to the wood - the darker wood is denser, while the lighter blond sapwood is less dense.
The size of a kalimba dictates the range where it resonates best. The Treble's smaller box means that it doesn't resonate so well with its lower notes. The Treble's lowest note in standard tuning is a B, and if you tuned it one step down to the A, you would lose good resonance on that note. The Alto's lowest note in standard tuning is a G, and similarly it will not be at its best resonance if tuned down to the F. In spite of this, I still thoroughly enjoy playing my two favorite alto and treble kalimbas with the Treble's low note tuned down to a Bb, and the Alto’s low note down to F. Kalimba Magic retunes a fair number of these kalimbas in this way.
The Kalimba Magic “Sweetheart Deal” is a Treble and an Alto kalimba together, both in standard G tuning. The "Matched Pair” is also a Treble and an Alto kalimba, but tuned so the Treble is an octave above the Alto. These come in G, F#, F, and in E. Both are great ways for you to play sweet music with your sweetie, and both are offered at a substantial discount.