Browser-local PDF jobs vs hosted PDF suites
Smallpdf and similar suites offer deep features, accounts and cloud storage. TCB PDF tools (Merge, Split, Compress) process in the browser with pdf-lib / pdf.js, page thumbnails where relevant, and honest size/page caps.
Use a hosted suite when you need OCR, e-sign or team libraries. Use TCB when you want a fast private merge/split/compress without an account. Read the privacy proof panel on each file tool after a job.