In fact Spath & Schmahl but also their colleague Berner from Regensburg (Berner later in Hamburg) were the main makers of the Tangent piano which made tangent pianos almost always the same, specially their action, dampers, Klangänderungen (Hand stops or kneelevers operating sound effects) but apart from these 3 makers there were many more who were organ or piano makers but also occasionally made tangent pianos.
Some of them are uknown makers or local instrument makers in the North Italy. Among them Baldassare Pastore is probably a more important maker (according to his craftsmanship and quality work).
In England there were a few exceptions of either originally made tangent pianos or later converted like a Beck square piano or Longmann & Broderip tangent piano.
Apart from these, there were many more converted harpsichords and spinets or square pianos to tangent action pianos, some with intermediate lever (which made them sound nearer to Spath's standard tangent action) or some without the intermediate lever being very simple action (just like a harpsichord jack jumping up but instead of plucking the strings from right or left hitting the strings from below)
These converted tangent pianos had sometimes not only the too simplified action model which can not be compared to a real Spath tangent action but they also didn't offer those several (and their many mixtures) of stops.
In the 19th century, even up to the middle of the century there were (specially in Italy) square pianos made with tangent action (or later adopted) with leathered tangents or even with thick layer of felt on their head!) which meant to sound like a normal fortepiano, so the didn't offer any stops.
Here are a number of them listed by Dr. Giovanni Di Stefano.