To be more specific I would say I have and not at the same time.
I have regretted it because for btec it needs too much time on assignments, deadlines to make sure you get a distinction or merit in each assignment as even if one assignment in a unit is a pass then the overall grade of that unit is a pass. Sometimes it gets so confusing on what to write in the assignment and what not you have to make sure it's in your own words and keep the plagiarism percentage less than 30% cite and reference properly each resource you use. Not so many online resources and past papers assignments examples available literally it's very hard to find one while on the other hand for a-levels you have one exam only at the end of the year and there a ton of resources available online. Also, not all unis accept btec and some may accept it but have some specific unit requirements or want a specific grade in specific units and some do accept but with a science a level. Like my friend, she is applying for biomedical science she wanted to go to kings college or queen mary but they straightforwardly rejected her as they require a science a level with btec.
But the advantages of doing a btec are that you get used to assignments, time management how to reference how to do your research etc. Basically, in uni, most of your work will require these skills so you are prepared for it a thing which a level students will struggle with. Another advantage is that a level students have to cram up everything for one exam if they got the grade ok if not they have to resist like another year. But in btech basically while doing assignments you don't have to cram up anything you do your research, read articles watch videos basically you understand the content to be able to write and explain it in your own words, you can do a resub if you are near the criteria and also ask for help from a teacher, classmate, a friend when doing the assignment for the part you don't understand like what are you supposed to do (but remember you cant plagarise like write word to word ). Also, you have 2 exams in both years. Year one exams i found are fairly good if yous study year 2 are a little hard but if you study hard you can manage it. You also have the opportunity to resit at the end of the year .e.g in year one exams take place in January you get your grade in march and can resit in May/June again which can boost up your grades for your results in august .same goes with year two. So basically you get the chance to improve your grade throughout the year something you don't get in a level.
In a conclusion, it depends on the person itself what type of learning they want and what suits them. Some people combine applied science btec with a level it can be anything like bio, chem, maths, psychology or sociology. While most of the people who take btec are the people who don't have the grades for a science a level so btec is an alternative route to go into sciences and healthcare which a wide range of universities do accept. So I would say if you have the grades go with a level as they are more recognisable.If you don't have the grade you can take a btec and an a-level alongside which do meet the grade and like it You can also take btec applied science alone as well as if you have a good grade in it you can get into a wide range of professions.
I personally really like the course and enjoy doing it they were some moments when I was like why did I choose btec but there are also many more times i don't regret it .( i would tell you the best at the end of the year before the results as I would know my grade for most of my units I can roughly estimate what my grade will be this is really useful when choosing my firm and insurance choice ).
Also, very important information all the things I told you above is what happens in normal times but since last year due to covid exams were cancelled, some assignments we also cancelled and they gave us predicted grade which is a total mess up . I don't even know what gonna happen or how are they gonna calculate our exam units this year so I am not giving any comment on that.
If you have any other question feel free to ask .Hope this helps