Salaam. I shall try my best to answer your questions:
Q- Is halal sausage actually halal and halal approved?
My A- There are several varieties of 'halal' sausage sold in UK, either by large companies or individual butchers and enthusiasts. There is now even a specialist halal sausage company, with details of that at the end of my post. Some are 'halal approved' (i.e certified by one of the several UK, EU or Global certification systems). Which certification system you follow is a personal choice. The majority of Muslims around the world still trust that a product is halal if the seller claims it is. Currently, no single certification system is agreed upon by all, so ultimately no system of halal verification can be considered 100%. It is too subjective a process.
Q- What is it made of?
My A- The majority of halal sausages being sold today in UK are made from a mixture of chicken, turkey and beef meat. However, there are also venison, lamb and turkey available. Non-Pork Sausages must by law contain at least 30% meat, to be classified as a 'named sausage'. i.e. If you sell a BEEF Sausage, it must contain at least 30% BEEF meat. The rest can be chicken, turkey or other meat/ non meat products. Mixing meats is common with most major halal sausage companies, because chicken is cheaper than beef. So, sausages with 30% beef and 30% chicken are common, and legal to call a BEEF Sausage. There is also much leeway regarding the type of meat cuts. Many cheap halal sausages contain 'mechanically retrieved meat' or 'mechanically separated meat'. These are considered the dregs of the meat industry. They have to be heavily flavored to become palatable. Sadly, most halal burgers, donor kebabs, chicken nuggets and sausages are made with this type of 'meat'. Personally, I never buy these 'mechanically recovered' products. If a halal sausage claims to be '70% meat', that does not mean it is 70% of one meat. It can be a mix, and also the piece of the chicken or cow you use can also vary. It may not always be the pieces which you would buy and cook at home !
Sausages must contain 'fillers' like breadcrumbs, otherwise they become too dry and kebab like. Also, preservatives are required by law.
Q- Why is it called sausage?
My A- The English word 'Sausage' is from the old french word 'saussiche', which in turn is derived from the Latin word 'salsus' which means 'to salt'. This reflects the long history of preserving meat using salt, in times before cooling systems and modern chemical preservatives were available.
Q- Should Muslims eat halal sausages or is there a problem with this?
My A- Yes, of course Muslims can eat halal sausages. By definition, a HALAL sausage is lawful and permitted under Sharia regulations, as the ingredients will be halal. Further, you should eat halal sausages if you like the taste !
Q- so why should it be an issue (if there is an issue) to eat halal sausage? Why must we frown upon halal sausages?
My A- I don't think it is a a big issue, but there are some Muslims who associate sausages with Pork meat, or they doubt the contents. Interestingly, the first sausage recipe ever recorded was from 5,000 years ago in Sumeria (modern day Iraq), and many Muslim cultures (Turks, North Africans) have enjoyed sausage for hundreds of years. Regarding the contents, one has to trust the vendor. Its the same as walking into a 'halal butcher'. 99% of the time, you simply trust that the person is selling you halal products. Some people have abused this trust, hence the proliferation of certification schemes.
Q- Has anyone experienced eating sausages?
A- Yes ! My family and I have been eating halal sausages for years, and so do thousands of Muslims around the world. Hundreds of thousands. A good quality halal sausage is tasty, full of really good pieces of meat, comforting, simple and versatile. 'Good quality' is the key. Too many halal sausages are made from poor quality (but halal) meat. Most of them use meat which is intensively farmed, like battery chickens, and some people would argue that these sources of meat are not ideal for Muslims, even though 'halal' in the commonly understood sense (i.e slaughtered properly). The Prophet (PBUH) said many times, that we should not be cruel to animals and we should treat them well even at the time of slaughter. For me, 'halal' requires that the animal lived according to the guidance provided in Qu'ran and Hadith as well as slaughtered according to guidance.
Q- And why do not most Muslim take-away shops and restaurant sell halal sausages or are they scared of something?
My A- No, they are not scared. Many places do sell halal sausages, but pizza, fried chicken, sandwiches, kebabs and other Asian foods are still the main halal fast food sold by British Muslims to British Muslims. That is a reflection of the mass taste preferences. As time goes on, other products will become interesting to a greater number of Muslims.
As you can see I am very Serious about Sausages. That is because they are my hobby, my passion and my business. I hope I have managed to answer your questions. I urge you to seek out some high quality and ethical halal sausages, and enjoy them !