Являться means 'to be', and since 'to be' isn't used so much with the present tense, it can be easily omitted in the vast majority of cases (if not in all of them), especially in spoken language: Это является большой проблемой = Это большая проблема In the past tense: Это не являлось большой проблемой = Это было большой проблемой There isn’t any difference in meaning between those two, only stylistic one: являться is mostly used in formal/written style. It's roughly equivalent to 'to exist as...', eg: It exists as a result of ... -- это является результатом...

уместно звучит и так и так

Actually you can say both, but when you use the verb являться, the sentence sounds more formal.

well... yuo see, it's all about 'sounds great', 'sounds aukwad ' etc. Hues and shades. With some words it combines well, with other words not that well. The meaning is the same as 'is' .... But 'является' comes ONLY with nouns/adjectives/participles. For locations we have 'находится' instead: Вы в Бостоне. Вы находитесь в Бостоне.

3. (!) We have so called 'short' forms of adjectives. "Бесплатна", "напечатан", "красив" (vs. "красивый"). This forms in general take function of "is + full-form". Bun not all of them are equally possible! "Бесплатна" (for my ear) sounds slightly better than "бесплатен"(NB!), "красен" "зелен" "чёрен" are rare/archaic, while in contrary 'красив' is used more often than 'красива'. But when one uses the full-form of a word, those who listen might wait for continuation: "Он красивый...."->***aren't you going to say "он красивый человек"? *** So 'он бесплатен' just sounds less great itsels (see NB! above), 'он бесплатный' sucks for other reason and the guy choses formal 'он является бесплатным', which 4)) fits to pretty official anouncement he gives.